RECENT MEMOIRS ON FRESHWATER RHIZOPODA. 6 7

RESUME of RECENT CONTRIBUTIONS to our KNOWLEDGEof " FRESHWATER RHIZOPODA." Part III . HELIOZOA{Desmothoraca) and MONOTHALAMIA (Monostomata).Compiled by W. ATCCHER, F.R.S.

Desmothoraca, Hertwig and Lesser.In this group the skeleton is formed of one single solid

piece enclosing an inner cavity and with peripheral openings;at the same time it is distinguished from the single-chamberedtest of the Monothalmia by its homaxial fundamental form.

There is not any ground to regard the Desmothoracousskeleton to be, as it were, composed of individual pieces onceisolated and then fused into one hollow-globular entirety,but rather it must have been so ab initio, and in it the irregu-larly arranged apertures must have been preformed. Boththe known forms (one of which is now for the first timedescribed by Hertwig and Lesser) appertaining here possessa more or less elongate and slender stipes, on the upper endof which is borne the hollow perforate skeleton containingthe living body-mass, and the lower end of which is attachedto some external support.

Hedriocystis pellucida, Hertwig and Lesser (this Journal,vol. xvi (1876), PL XXII , figs. 21 and 22),

is characterised by the possession of a stipitate, single-cavitied skeleton. The stipes (005—0075 mm. long) (fig.2\, s) is attached by its dilated base to algal filaments andsuch like foreign bodies, whilst the upper end passes withoutany sharp limitation into the contour of the skeleton (fig.21, t). The latter is ovate-elongate and in the direction ofthe stipes, like it delicate and pellucid, and so constituted.that its wall, at all the places through which the pseudopodiapass, projects as so many pointed prominences, the wholelending to it the aspect of a knobbed club with stellate pro-jections. Except at the apices of these projections, which areperforate and destined to allow the passage of the pseudo-podia, the wall is otherwise closed.

The formation of the skeleton begins with the productionof the stipes (fig. 22, s), thereupon succeeded by the deposi-tion of the skeleton, and both by the agency of the protoplasm.When fully formed the round body-mass is freely poisedwithin the cavity of the skeleton, as if suspended by thepseudopodia. It consists of a finely granular protoplasm,and contains an oval nucleus (with nucleolus) (figs. 21 and

6 8 W. ARCHER.

22, n), whose length approaches one third to one fourth thediameter of the body; towards the margin of the latter occurone or several vigorously pulsating contractile vacuoles (figs.21 and 22, c c). The pseudopodia do not subdivide; theyshow a distinct granular current; sometimes even minutevacuoles could be seen passing up and down them.

As regards reproduction, the authors record simple fissionas readily to be observed. They frequently saw two bodiesof about equal size within one and the same shell, each pro-vided with its nucleus, and possessing its contractile vacuolea.Once they saw a small individual, which, no doubt, pro-ceeded from self-division, furnished with a minute stipes, butstill without a shell (fig. 22). The plane of division stoodvertical to the direction of the stipes. Besides subdivision,encysting occurs, but the authors were unable to follow outany further development.

Clathrulina elegans, Cienk.1 (vol. xvi (1876), PI. XXII ,figs. 23—25).

Cienkowski was disposed to regard the perforate hollow-globular skeleton of this now pretty-well known form ascomposed of numerous polygonal plates. This view Hertwigand Lesser seem rightly to contradict; it certainly seems tobe but a single connected structure throughout; the openingsare roundish-polygonal, and their margins surrounded by amore or less elevated rim, which in fully-grown examplescan be seen at the equatorial periphery of the sphere stand-ing off like papillae or very short blunt spines. The stipesis regarded by Hertwig and Lesser as tubular; so it cer-tainly appears to be, its base can be often seen to terminatein a number of rootlike processes by which it retains a holdon foreign supports, or indeed often on the shells of otherindividuals of its own species. As to the sarcode body as isknown, it is comparable to Actinophrys, but as the originaldiscoverer, Cienkowski (I believe I myself found it, however,considerably prior to him, and showed it at a meeting of theDublin Microscopical Club and this considerably in advanceof the date of my own paper, preceded by Cienkowski's onlyby a very short interval) observes, unlike that of that form,that here the peripheral contour passes into a number ofshort lobelike projections terminating in the pseudopodia.

Hertwig and Lesser distinguish between two kinds ofvacuoles—one enclosing food-particles, the other simple fluid-cavities ; the latter mostly projecting at the periphery in asomewhat hemispherical manner and are partly contractile.

1 Cienkowski: ' Archiv f. Mikrosk. Anat.' Bd. Ill, p. 311, t. xviii.

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The rounded nucleus (with nucleolus) is very difficult ofdetection, but it exists (figs. 21 and %%, ri).

As to Greeff's view of a homologue to the central capsulewhence radiate axial threads of pseudopodia, Hertwig andLesser are unable to concur in it. The pseudopodia are veryfine, granular and readily anastomose, which circumstanceHertwig and Lesser seem very justly to suppose is against theexistence of such threads; apart from the difficulty of detect-ing an inner thread within structures themselves, appearingunder even very high amplifications as themselves but merethreads.

The assimilation of the incepted food particles takes placewithin the vacuoles before alluded to, but a body too large topass inwards through the apertures of the shell may be sur-rounded by the protoplasmic substance of the combinedpseudopodia, and so digestion be carried on in a vacuole thusappearing as it were impromptu.

Hertwig and Lesser have followed out the modes of repro-duction described by Cienkowski:—After complete self-divi-sion of the body-mass the two portions pass out through anaperture of the shell, and at once establish themselves, first,producing a stipes, followed by the appearance of a shell. Afurther mode is by encysting, the body mass first breakingup into a number of individual portions, each by and bysurrounded by an externally spinulose membrane; after apause the cysts develope pyriform, nucleated, seeminglybiflagellate, zoospores, followed out by Cienkowski to the for-mation of young Clathrulinse. A third process was observedby Hertwig and Lesser, characterised by a repeated sub-division, and, in the formation of zoospores, it possesses a con-nection on the one hand, with the reproduction by encysting,and on the other, in the want of a membrane to the seg-mented portions, it is comparable to simple division. In allcases the authors found the body-mass within the shellbroken up into three portions, each of which appeared togive off pseudopodia. Of these fission-products, two weremutually alike in size and smaller than the third, whichlatter contained approximately about an equal quantity ofprotoplasm to that of the other two taken together. The firsttwo left the shell simultaneously, or at least one but a veryshort time subsequent to the other. As already described byCienkowski, during this process the organisms project anamoeboid process through one of the foramina of the fenes-trate skeleton, causing a figure-of-8- shaped constriction ofthe body during exit; this accomplished, the now free bodyforms an elongate ovoid zoospore, with a homogenous anterior,

70 W. AECHER.

and a granular posterior end (PI. XXII , fig. 23). In the formercould be seen the nucleus with its nucleolus, almost com-pletely filling it, and in the latter two or three contractilevacuoles; at the anterior apex appear two flagella as long asthe body, by means of which the organism advances with aslow and uniform rotating movement. After about half anhour or more it settles down vertically on some object, whereto develope its stipes, and whilst assuming a globular figure,continues, without advancing, to rotate on its longitudinalaxis. As soon as this has ceased the pseudopodia becomequickly developed on all sides, and the body passes into theform of a naked Clathrulina. About this time the stipesbecomes apparent as a clearly-shining, sharply-contouredcircle on the surface of the body (PI. XXII , fig. 24, s). If theorganism be brought into a profile view, it is seen that thestipes which becomes firmly attached to the substratum,soon growing to a considerable size, takes its origin in anumbiiicus-like depression of the body and forms a directprocess of the body-mass (Fig. 25). It thus originatesas a protoplasmic structure and only subsequently becomesdeveloped around it the tubular skeleton-portion of the per-manent stipes. In the progress of growth the protoplasmicprolongation filling the tube must become retracted, for inthe fully-formed Clathrulina the soft body-mass stands nowhere in connection with the stipes.

The authors were not able to follow out the developmentof the fenestrate skeleton, but doubtless it is preformed byprotoplasm, they at least found that some young individualsstill naked, but with stipes, showed the pseudopodia mutuallyunited by transverse connections; these forming, at a littledistance from the body-surface, beautiful arcades, most pro-bably the bases for the development of the future fenestrateskeleton.

Reverting to the larger subdivided portion of the originalbody-mass left behind within the shell, and which at firstmaintains its place therein, still displaying its numerouspseudopodia as if it were making an endeavour to make goodthe loss in body-substance which it had suffered, the authorsarrived at no definite results. In one case of which they hadunder observation, the object died from want of accession ofa fresh supply of water, after they had had it for a wholeday long under observation, without any perceptible altera-tion. On another occasion they found the shell empty, onrenewing their observations on the following day, but asthey saw two zoospores hovering near they supposed that thebody left behind (as described) had once more subdivided, and

RECENT MEMOIRS ON FRESHWATER RHIZOPODA, 7 1

that the products of such fission had passed into the state ofzoospoves. Should this procedure (i.e., the exit of all productsof subdivision) be the general one, the mode of reproduc-tion here described might be simply referred back to thatmode by fission described by Cienkowski—the only differencebeing that each product of division agaiu repeatedly sub-divides into two, and produces a zoospore. As regards bothmodes, analogies are offered by Microgromia.

That examples of this species are sometimes found seatedon preceding individuals, in which fact Greeff thought to seean "inclination to the formation of Colonies/' Hertwig andLesser regard as purely accidental; and in this they coincidein my own previously expressed opinion—such examples areseated on those preceding them in the order of time, simplybecause the latter afforded the nearest fulcrum for the youngindividuals resulting from simple subdivision without passinginto the zoospore-state, and hence capable of but a compara-tively very restricted locomotive power.

Having thus given a resume of the foregoing beautifulobservations of these authors on Clathrulina, one is temptedhowever, to urge that there hardly seems a necessity to placeHedriocystis pellucida, Hertwig and Lesser, in a separategenus—that the two organisms are indeed specifically mostdistinct, cannot for one moment be questioned. I almostthink this will be readily evident on looking at the authors'own diagnostic characters.

Hertwig and Lesser, in concluding their long and mostimportant work, regard it as proven that a separation of ourHeliozoa from the Radioloria is justifiable (and I must now,as before mentioned, give my own adhesion to the view), butthey point out several of the lacunae in our knowledge requi-site to be filled up, and certain vexed points to be settled byrepeated and extended researches, ere we have a completeand true conception of the whole of the conditions of organi-sation of the Heliozoa. Thus it would be desirable to know,How far a differentiation of the body-mass into endo- andectosarc prevails in the group—Whether a differentiation ofthe pseudopodiainto a granuliferous investing stratum arounda homogeneous axis is a more widely spread character thanwould as yet appear—What the mode of ending of the axisand its histological significance, and last (not least)—Whatthe bearing and details of the various reproductive processes ?The classification (propounded by them) of the group can hencebe regarded as but provisional, the more so as the relativelysmall number of genera and species does not yet render it

7 2 W. ARCHER.

practicable to do for the Heliozoa what Hackel has done forthe Radiolaria and Carpenter for the Foraminifera.

Previous to entering upon the recently described accessionsto the Monothalamatons Sarcodina, appertaining to thefresh water, two very distinct forms found in sea-water,having Actinophryan resemblances, to say the least, claim abrief notice.

Actinolophus pedunculatus,Eilh. Schulze1 (Plate XXII, figs. 26, 27, vol. xvi, 1876).

Though marine in habitat the form named above seems toclaim a notice in the present resume. Seated on varioushydroid Polypes, and even on sea-weeds, the author foundat various times of the year, but mostly in summer, thisremarkable stipitate animal form, in outer habit resemblinga Podophrya occurring in its company, but in no way belong-ing to the Acinetse, but truly appertaining to the Rhizo-poda.

The stipes is cylindrical (length, 006 c. O'l mm., breadth,0-003 — 0-004 mm., figs. 26, 27); without any basal plateor expansion of any kind; its lower end stands directly uponthe substratum, whilst at the upper end it bears the body.It is perfectly colourless and hyaline. The author concludesfrom the outer layer appearing doubly contoured that itconsists of a delicate tubular sheath of chitinous nature,enclosing slight refractive contents. In the interior a few,usually three, mutually equidistant parallel fine lines canbe seen mostly running longitudinally through its wholelength; but in some cases confined to the upper portion ofthe stipes only (figs. 26, 27).

The body borne at the apex of the stipes is usually pyri-form, its narrower end downwards (fig. 26), but the by nomeans inconsiderable contractility of its mass enables it toassume various figures, from ovate to globular. Apart fromthe pseudopodia it is always smooth and of a simple contour(length, 0-02—0-03 mm.; breadth, 0-015 mm.). Thehyaline plastic (" zahfliissig ") basic substance (as is usual inSarcodina)shows numerous fine and coarse more or less re-fractive granules embedded therein. The author could notperceive any special membrane nor any ectosarc. In theinterior occurs constantly a nucleus, which strikes the eyeas much by its extremely large nucleolus as by its excentricposition (fig. 26). The oval rarely globular, homogeneous,and rather strongly refractive smoothly-contoured nucleolushas a diameter of about 0003—0-004 mm., and shows around

1 Sclmlze, 'Schultze's Archiv,'Bd. X, p. 392, t. xxvii, (T. 1—9.

RECENT MEMOIRS ON FRESHWATER RHIZOPODA. 73

it a narrower clear granuleless envelope, whose outer contour(corresponding probably to a membrane) is only rendereddistinct after application of acetic acid, then appearingdoubly contoured—in living examples, however, alwaysclosely encompassed by the granules of the surroundingsarcode. The nucleus never occurs central or indeed evenwithin the broader portion of the body, but constantlyplaced in the narrower basal part, and here not in thelongitudinal axis, but laterally (fig. 26).

But in the centre of the anterior broader part of thebody a structure is to be perceived, as to the nature ofwhich the author has not been able to gain any certainty.It appears as a dark globular body of about O'OOl mm. indiameter, and mostly, as regards its position, corresponds tothe common centre of the pseudopodia (fig. 26). Some-times, indeed, the author thought he had perceived finelines therefrom to the pseudopodia, but could not makehimself certain of the existence of such; neither could hedetermine if the fine lines running longitudinally throughthe stipes were continued into the body.

Sometimes particles of an orange colour could be per-ceived in the body - substance; these were not like therounded, smooth, often coloured, granules of many Heliozoa,but appeared as minute irregularly-shaped rough fragmentsof various sizes, and occurred not in the darker centre, butonly in the outer granular region. They sometimes occurin great quantity, when they impart a brownish-red colourto the body; sometimes they are very wide apart, and againthey are wholly absent.

Crude food was seen only seldom, then lying in the outerpart amongst the colouring granules.

The author never saw any pulsating vacuoles.The pseudopodia are numerous, but occur only at the

outer and upper part of the body, never close to the stipes.They are very fine, long, and pointed. On a thin axilepart there hung granules and clusters of finely granularsubstance. Whether there be really a more solid axilethread present, the author could not decide, though of thatimpression. A fusion of pseudopodia he had seen in onlya few cases; and that only due, as it would seem, to somemechanical shock or during the capture of some foreign bodyas food. The author was struck by the fact that they neverseemed to become wholly retracted into the body-mass;no doubt a considerable amount of contraction under certaincircumstances took place, always stopping at a certain point,or nearly equidistant from the body, so that they would

7 4 W. ARCHER.

form a kind of crown around it, each apex showing anagglomeration of contracted granular sarcode, lending a con-siderable amount of resemblance to certain Podophryans.The author, to account for this phenomenon, was disposedto assume the presence of an extremely hyaline, thoughimperceptible, gelatinous envelope surrounding the appa-rently naked body, preventing the abrupt retraction of thewhole of the pseiidopodia and causing the agglomeration ofthe granular substance at its periphery.

But, as well as the examples as above described, othersoccurred with a distinct outer covering, and at the same timeother alterations were perceptible, possibly indicating aresting condition preceding a subdivision. A perfectlypellucid gelatinous envelope directly and everywhere sur-rounds the body, permeated by fine dark parallel lines pro-ceeding from the stipes and becoming lost in the body-sarcode. A more advanced stage could be seen in othercases in which a layer of delicate fine strongly refractiveplates could be recognised on the surface of the gelatinousinvestment (fig. £7). By degrees these seem to becomethicker; their contours, however, not yet marked out by themore evident, presently showing themselves as solid,tolerably regularly hexagonal plates. Taken altogether, theyform an approximately globular, ovoid, or pyriform case,prolonged into a similar coating down the stipes. It isstriking that these plates do not touch by their lateral mar-gins, at least the author always saw clear intervening narrowzones, which could only be interpreted at intervalsbetween isolated plates or as thinner parts of a continuousmembranous coat. Owing to their withstanding concen-trated sulphuric acids the author concludes they are sili-ceous. Whether when fully formed the old stratum ofgelatinous substance still remains the author could not satisfyhimself.

Further modifications consisted in the subdivision of thenucleus, regularly preceded by an elongation, an assumptionof a biscuit-shaped figure and final breaking up into twoportions, each surrounded by its own special hyaline envelope(fig. 27). The two newly-formed nuclei how recede from oneanother. At the same time the pseudopodia may remainquite unaltered and fully extended, even though the distinctrudiments of the plates were present (fig. 27). But withthe further development of the plates the pseudopodiabecame wholly retracted, and at the same time the littledark globular central body disappears. From the lattercircumstances the impediment to the nucleus attaining the

RECENT MEMOIRS ON PRESHWATER RHIZOFODA. 75

middle region of the body seem to be removed, for nowthe two nuclei can be met with at any part of the body.

The " encapsuled " examples mostly appeared to possessa shorter stipes than the naked, but the author did notfeel certain whether there was any real contraction or thatshort-stalked forms were more prone to become encap-suled.

The connexion of the axial inner portion of the stipeswith the body, by means of the longitudiually runningparallel lines, is ever maintained ; these could be followedsometimes, even up into the sarcode body-mass (fig. 27).

Any further data as to a subsequent subdivision or othermode of reproduction the author's opportunities did notafford him.

Whether this interesting form might possibly coincidewith Lecythia elegans (Strethill Wright)1 the author couldnot determine. There is a considerable resemblance in thestipes, and on the capitate figure of the pseudopodia onbecoming retracted; but the figure of the body of that formdrawn out at its outer extremity does not agree, nor doesthe statement that it is enclosed in " a closely-fitting enve-lope." More closely related possibly to Zooteira religata(Strethill Wright)3 would appear the present form; thatform, however, possesses a short mucous covering surround-the basis of the stipes into which the whole animal can befully withdrawn, having a thick muscular band with lateralprocesses in the stipes; it possesses also a granular region,designated by Wright as ectosarc, surrounding the richlygranular but non-nucleated body (endosarc), from which thepseudopodia are said to proceed.

Lithocolla globosa, Eilh. Schulze3 (PI. XXI, fig. 9, vol.xvi, 1876).

Whether the form called Lithocolla globosa by EilhardSchulze, and found by him in the washings of some sea-weeds and mussel-shells from the Baltic, really belongs tothe Heliozoa or not, is, so far as the author's experience ofit reaches, still undetermined. Were it so it would probablyjustify the formation of such group of which it would betypical, characterised by the heliozoan inclosing itself aroundby a more or less loosely apposed stratum of foreign are-naceous and other foreign particles, comparable in a measureto that of DifHugiEe, but not coherent into a " test."

1 S. Wright, 'Ann. Nat. Hist.,' vol. viii, p. 123 (1861).2 S. Wright, 'Quart. Journ. Micros. Sci.,' vol. ii, p. 217 (1S62).3 Schultze's ' Arcliiv,' Bd. X, p. 389, t; xxvi, f; 8—10.

76 W. ARCHER.

When the author's attention was first called to the Sar-codine in question, the object before him appeared hardlymore than an accidental globular agglomeration of sand, nor,until this at first sight scarcely noteworthy little mass beganto move spontaneously, did he perceive the fine linear pseu-dopodia projecting around from between the sand particles,and realise the fact that a living organism really lurkedinside.

To judge from the figure and from the author's descriptionof the mode of motion fixed on the pseudopodia, this formreally appears to have the aspect of a heliozoan so encom-passed by foreign arenaceous particles, but on pressure theauthor found that these did not form a connected test, butwere only more or less loosely applied, whilst at same timethe sarcode body then assumed the appearance of a discoidor elongate mass; continued pressure caused the whole topass into a shapeless commingling of softish finely granularsarcode, with the sand-particles now embedded therein.

In the ordinary condition the pseudopodia are long (aboutdouble the body-diameter), extremely fine, linear, radiallyextended, rather rigid, and never inosculating; mostly theforeign particles lie closely applied to each other, allowingno very perceptible interspaces; but sometimes only a com-paratively few are present (occasionally a few diatom frus-tules), leaving considerable vacant interspaces. The body-mass appears usually to have shown a reddish-colour whenclosely surrounded by foreign particles, but to have appearedcolourless when these were few. But unfortunately theauthor was unable to gain any insight into the body-struc-ture, not even to discover if it possesses a nucleus. Of courseon the result of further investigation in this regard dependsthe reply to the query as to the proper location of thissarcodine.

MoNOTHALAMIA.

Under the designation Monothalamia are comprehended alarge group of Sarcodina, with such pervading community ofstructure that no difficulty can be felt in regarding them asforming a related group proceeding from common primordialforms. Hertwig and Lesser after giving at some length theviews of the older authors, and a resume of the gradualgrowth in our knowledge of their characteristics, and afterdescanting upon the clearly proven untenability of any realdistinction between simple vacuoles and contractile vesicles,formerly regarded as of considerable importance, proceed topoint out the great distinguishing feature, owing to which

RECENT MEMOIRS (JN FRESHWATER RHIZOPODA, 77

their separation as an independent group becomes necessary,and that is the monaxial character of the body, enclosed in asingle-chambered usually firm and unyielding test; at one orboth ends of the test it possesses a definite and permanentopening for the emission of the pseudopodia. The axisleading therefrom to the opposite side the authors designatethe principal or longitudinal axis, although it may in someforms be shorter than that transverse thereto. If the twoaxes are alike the test, viewed from either end of its "longi-tudinal" axis, will be circular, a simple monaxial fundamentalform ; if they are unlike the monaxial fundamental formbecomes bilaterally symmetrical. In this monaxial funda-mental form, then, of which the bilateral symmetry is but asecondary differentiation, consists the pervading distinctionof the Monothalamia from the homaxial Heliozoa. The testis either a pure secretion product of the organism where it iseither smooth or of variously ornamented peculiar structure,or it is built up or partly composed of foreign constituentssuch as arenaceous particles, diatomaceous frustules, &c,cemented together. The pseudopodia proceed outward fromthe animal within only through the one great frontal openingthrough which, of course, is carried inwards from withoutthe food, or such an opening occurs (in a very few forms) atboth ends (Amphistomata); if (as mostly) there be butone opening that extremity may be regarded as the frontalor " oral," the opposite closed end as the " aboral" (Diplo-pola, Hackel), whilst when there are two openings theyappear to be equivalent and there is no evident differentia-tion of the poles (Haplopola, Hackel). Still so far as Ican see the pseudopodia do appear to be usually given off,notably more copiously and to reach a greater length at oneend than at the other.

The body-mass never advances beyoud the dignity of asimple cell; in the Monostomata the posterior part is usuallythe more homogeneous and contains the nucleus ; the anterioris the more granular, and usually presents some vacuoles,often contractile. In the Amphistomata the nucleus occupiesthe middle point between the two openings. In the multi-nucleated Arcellae the nuclei lie towards the margin of thediscoid body.

The pseudopodia are of multitudinous character in thedifferent genera or species. They are cylindrical, blunt, un-branched, non-coalescing, granuleless, very slow in action,on the one hand, or delicate, linear, or inflammatory, pointedacutely, much ramified, constantly coalescing or highlygranular and presenting an active " circulation" and vigorous;

78 W. AKCHER.

contractility on the other; between such most varied inter-mediate conditions occur, or these characteristics may becombined in the most manifold but seemingly ever charac-teristic, manner. Still they all readily enough fall underone or other of the two great categories designated as Rhizo-podous and Lobose.

As to reproduction—simple division formation of zoospores,and encysting have been observed.

The unexpected and very interesting discovery of theForaminiferabeing?mcZea£ec£Sarcodina, made simultaneouslyby Professors E. Schulze and R. Hertwig—an abstract ofwhose recent papers is given in another part of the currentnumber of this Journal (which see)—imparts afresh interestto our freshwater Monothalamla, which are thus shown tohave a direct relationship to the marine forms throughGromia, &c.; they are, in fact, Imperforate Thalamophora.

Monothalamia Monostomata.

In the discrimination of subgroups no characteristics areseemingly more important than those presented by the pseudo-podia, but those possessed by the test as regards its structureand its figure are of considerable value, in some forms more sothan in others—the structure being more of generic, thefigure more of specific importance.

The test itself may be discoid, cylindrical, or flask-shaped,whilst the monaxial fundamental form may be further deve-loped to a bilaterally symmetrical one, which modificationmay be brought about according toone or other of these modes :

(1) An axis vertically transverse to the " longitudinal"may surpass the rest in growth so that the test becomesbroader in this direction, and hence laterally compressed(thus Plagiophrys scutiformis,' Hertwig et Lesser, withits smooth test, or Euglypha compressa, Carter, with a testformed of superimposed imbricated plates).

(Si) That portion of the test terminating in the " mouth"grows to one side, which thereby comes to lie more or lesslateral. (Thus Microgromia socialis (Arch.), Hertwig, witha smooth test, or Cyphoderia margaritacea, Schlumb., withtest similar to Euglypha).

(3) The principal axis of the test undergoes a curvature(thus the snail-shell-like test of Diffiugia spiralis).

These specialities of outward configuration are valuablespecific characters, if not available for the formation of generaor larger groups. The presence or absence of special struc-ture in the test itself and the presence or absence of foreign

RECENT MEMOIRS ON FRESHWATER RHIZOPODA. 7 9

bodies in its constitution are seemingly of more importancein the formation of genera, whilst as regards larger groupsthe authors are driven back to the characteristics possessedby the pseudopodia as the most comprehensive and promi-nent, and at same time natural and constant, as already longago laid down by Dujardin and Carpenter : these are the twogroups known as Lobosa and Rhizopoda.

Monothalamia Lobosa.

The pseudopodia are either cylindrical or finger-like, orform broad plates or lamellse, or they end in a conicalmanner. They are always blunt at the apex, never very long,rarely and but slightly branch, their protoplasm homogeneous,very rarely any granules passing into them and then onlynear the base.

The test is either a pure secretion-product or formed bythe cementing together of foreign bodies.

Arcella vulgaris (Ehrenb.)

For the first time seemingly a correct description of thestructure of the peculiar test of this somewhat variouslyshaped and otherwise pretty well known, and at least common,species is given by Hertwig and Lesser.1 Two plates, anouter forming the superficies of the test, and an inner appliedto the body of the Arcella, are united by a honeycomb-likestructure, whose hexagonal cavities form prismatic spacesstanding vertically to the surface. These spaces the authorstook to be filled with fluid; in order, however, to test if realhollows or cavities the authors applied a solution of carbonateof soda, adding thereto acetic acid, subsequently washing outwith water: the hexagonal spaces then for the most partbecame filled with air and therefore appeared with the blackborder indicative of that condition. They therefore concludethat the appearance of the marking on the Arcella test is notdue to granulation as Dujardin supposed, nor to perforatingcanals as held by Ehrenberg, nor built up of individual platesas Claparede and Lachmann, as well as Carter, assumed.Wallich, indeed, spoke of a " symmetrical reticulation" and of" hexagonal interspaces ;" still Hertwig and Lesser doubt ifhe altogether correctly appreciated the structure, as how other-wise could he come to the surprising conclusion that Arcellavulgaris could be but a subspecies or even species of Difflugia ?A query which I may venture heartily to re-echo.

1 Loo. cit., p. 93 et seq.

8 0 W. ARCHER.

In the body-mass occur several nucleolated nuclei and con-tractile vacuoles. Encysting sometimes is met with, but nofurther development has been noticed. The so-called " con-jugation" accompanied with a kind of rhythmical temporaryinterchange of the plasma is a common phenomenon, inter-preted by Hertvvig and Lesser as merely the expression of anact of division, inasmuch as so frequently one of the indi-viduals is of the deep reddish-brown of the mature form, theother yellowish or colourless, the latter presumably theyounger j the two individuals presently separating and each"going its way."

Since Hertwig and Lesser's work, however, Biitschli haspublished a memoir,1 in which he seems to return to the viewthat the conjugation has, at least, sometimes, a greater signi-ficance than merely the expression of an act of division. Hefound (as sometimes happens) three all alike highly colouredindividuals conjugated; afterwards, when separated, theseshowed a portion of the body-mass broken up into a number(as many as nine) of minute " Amoebae," with nucleus andcontractile vacuole. These made their way out from theparent-test, and Butschli supposed them to be germs ofyoung Arcellse, but was not able to follow out their develop-ment any further. How such amoeboid germs develope testsand become Arcellse is uncertain, and, adds the author, "thiswould be of great interest, for I can hardly suppress thedoubt that such forms as the PseudocJilamys patella, Clap,et Lachm., and the Arcella patens of the same observers,may not belong to the development-cycle of Arcella vulgaris."This latter view I venture to hold, with Hertwig, as alto-gether unfounded.

1 0. Butschli, " Zur Kenntniss der Fortpflanzung dei, Arcella vulgaris,"in ' Schultze's Archiv,' Bd. xii, p. 459, t. xxv.

{To be continued.)