AuGCsr i6, 1900 J 



NA '1 URE 



405 



hand and from ilie formed nucleus on the other, and 

 applied to thpm the name clirnmidia. They consist of 

 groups of granules or branched strands of a substance 

 staining wiih the same rcagenis as the chromatin of the 

 nucleus. In Aciinosph.erium, in which Herlwig first recog- 

 nised them, Ihey are normally present in the prot(jplasm, 

 but their number is increased in particular stales of the 

 b(xly in relation to metabolism, as bv over-feeding, but 

 also, it was found, by starvation. 'The chromidia are 

 derived from the nuclei, and indeed in certain circum- 

 stances the nuclei may completely resolve themselves into 

 chromidia. A siruclure present in ihe body of many 

 shelled Rhizopods, and regarded bv llernvig as of the same 

 nature as Ihe chromidia, is the chroiniJial iicl. In Arcella 

 this lies in Ihe peripheral pans of the disc-like bodv, and 

 sends reticulate processes into the rest of the protoplasm, 

 the chromidia it stains with chromatin stain= 



l.ike 



Hertwig concludes that in Arcella Ihe two or three nuclei 

 originally present may, in a certain phase of the life- 

 history, completely disappear, and that in that case nuclei 

 are formed afresh by the aggregation of chromatin malerial 

 ■ .nbout new foci in Ihe chromidial nel.' A similar chro- 

 midial net was described by Herlwig in Kchinopvxis. In 

 the following year Schaudinn - pointed out ihat the 

 chromidia and chromidial net of llfrlwig were compar.ible 

 wilh the siTands of siaining substance which had been 

 de^cnbed in thi- l'"oraminifera. In tracing out the verv 

 inten-sting life-hislory of Onlropyxis he showed thai as 

 m the Koraminifer.i, the nuclei of' the gametes are derived 

 from [he chromidial nel, while here also the vegetative 

 nucleus disappears. fomp.-ir.ible structures were also 

 -hown 10 exist in Chlamydophrvs, a species of Amceba 

 and in Entama'ba." Schaudinn found Ihat in all the cases 

 investigaled by him the nuclei of the gametes are derived 

 from the chromidia, whether diffused or united into a 

 reticulum, and concluded that the chromidia are in fact 

 the subsl.incc of the nuclei of the sexual cells. He .dso 

 in-iiluled A very enlightening comparison wilh Ihe 

 Infusoria, ihe macronucleus of which, formed at llie 

 division of the zygote nucleus and disintegrating prior to 

 conjugation, he compared with the vegetative nucleus of 

 the Rhizopoda, while the micronucleus finds its homologue 

 in |he more or less dispersed chromidia. 



Ry this comparison a number of i)reviously isolated 

 phenomena fall into line. The nuclear apparatus of the 

 Infusoria, differenliated into vegetative and reproductive 

 portions, finds, though not an explanation, at least a 

 parallel in other groups of Protozoa. The scattered 

 chromidia of the l-'oraminifera are thus connected with 

 the chromidial nets of monolhalamous Rhizopods, which 

 present various degrees of compaclness, and through them 

 with the definitely rounded Infusorian micronuclei. In the 

 involved streaming movements which precede the separ- 

 ation of Ihe protoplasm of the microspheric parent into 

 the inegalospheric brood we mav recognise a process of 

 equal distribution of the minutely divided chromidia 

 through all parts of the mass whic'h is about to divide, 

 leading lo iheir transmission in equal portions among Ihe 

 offspring. 



The fact Ihat in the Foraminifera. at anv rate, the 

 chromidia are directly derived from the vegetative nuclei, 

 though they increase in size independently, is at least 

 some acknowledgment of the hereditary principle in the 

 transmission of nuclear material, though we have at pre- 

 sent no evidence whatever to show that the foci about 

 which Ihey gather to form Ihe nuclei of the megalospheres 

 or the moiher nuclei of the zoospores .are irT anv wav 

 -derived from preexisting nuclei. 



Though light appears ahead, it seems lo me ih.it we 

 are not yet at liberty to consider out-selves out of the wood. 

 The comparison of chromidia wilh infusorian micronuclei 

 has brought us a long way from Hertwig's original observ- 

 ations in .'Kctinosphsrium of the dependence of the form- 

 ation of the chromidia on slates of metabolism : moreover. 



1 R. Hertwig, "IJeb. Kncyslierung u. Kernvermehrune bei .ArcelLi 

 vulgaris," Kupffer's /•'«,'..,//)•//■/. iSog. 



- ■■ Untersuchuneen lib. d. Fortpflanzung einiger Rhizopoden," .h/: am 

 ,/. Kais.Ccnimiluitsiinilc^d. x\\., :,, !^7,. 



3 Calkins in his very interesting observations on Amoeba J-ioUits aki 

 found thai the cbromidium-like bodies arc derived from the vegetative 

 nuclei. See his paper. •' Evidences of a Sexual-cycle in the Life-h^tory of 

 Amce'tiprslcus.- Arch. f. Pro!htinliun,ic,Y.A. \. W. (1904). 



NO. 1920, VOL. 74] 



no evidence has as yet been found that in Actinosphierium 

 the gametic nuclei are formed from chromidia. 



In comparing the abundant deeply-staining chromidia 

 of the Foraminifera with the Infusorian micronucleus, so 

 poor in chromatin, Schaudinn ascribes the difference to the 

 fact that in Ihe former, as in Rhizopods in general, the 

 formation of the brood (of zoospores) occurs by simul- 

 taneous multiple fission, and is connected wilh the act of 

 fertilisation, so ihat sufficient chromatin to provide for 

 the nuclear equipment of each of the thousands of zoo- 

 spores must be ready in Ihe parent as it approaches the 

 reproductive stage. In ihe Infusoria, on the other hand, 

 where Ihe gametes are the ultimate product of a succession 

 of binary fissions there is never the occasion, at any one 

 time, for so large a store of chrom:ilin in Ihe body.' 'While 

 admitting that there is much force in this explanation, we 

 may notice Ihat in I'olyslomella ihc formation of ihe 

 chromidia begins e.irly in the growth of the microspheric 

 individuals, and they .are in my experience verv promin- 

 ently present in full-grown specimens of this generation, 

 although Ihe sexual nuclei are not formed until the next 

 or megalospheric generation has reached maturity. It 

 would appear, Iherefore. Ihat in Polyslomella the chro- 

 midia are .associaled wilh ihe formation of Ihe nuclei of 

 Ihe reprodui live elemenl^, whelher these do or do not 

 engage in conjugation. 



Ooldschmidl,- in a very capable review of our know- 

 ledge of chromidia, is inclined, on Ihe ground of the 

 apparent difference in relation to the life of the organism 

 between the siruclures so called by Herlwig, in .\ctino- 

 sphicrium, and the chromidial nets and strands of Rhizo- 

 pods, to the view that two physiologically distinct elements 

 have assumed a morphological similarity and mode of 

 origin. While retaining ihe name chromidia for ihc 

 former, he dislinguishes the latter under the name Sporetia. 

 It is, however, perhaps somewhat early at present lo insist 

 on this distinction. Hertwig's essay has already been most 

 fruitful in results, and we cannof doubt thai (lie nature of 

 ihe chromidia will be further elucidated now ihal allcnlion 

 has been directed to them. 



The rclatinii in si:e hvlwccn Ihe microspheric parent und 

 the members of the megalospheric bruod. 



There is one other point lo which, before concluding, 

 I wish to invite your attention. 



In the course of the discussions on the significance of 

 the occurrence of nummulites in pairs, objection was taken 

 to the view that the members of the pair belonged lo the 

 same species on the ground that solitary forms — megalo- 

 spheric or microspheric, unaccompanied by the usually 

 associated sister form — occurred in certain localilies. De 

 la Ilarpe himself, having at first urged this objection, 

 withdrew it; but it is still entertained by some pala'onto- 

 logists, and made the ground for maintaining Ihe view 

 that the members of a pair are specifically distinct. 



On looking into the matter I found that two out of the 

 three species of Nummulites which occur in the Brackle 

 sham and Barton beds in the Ihimpshire basin were only 

 known, so f.ir as published descriptions went, in the 

 megalospheric form, although the corresponding micro- 

 spheric forms had been found associated wilh these megalo- 

 spheric forms on the Continent. It Iherefore seemed worth 

 while to examine the Fnglish beds to see w'helher they 

 might lend any support to the view I have mentioned 

 The three English species arc the following ; 



Xummiilites laevigatas (Brug.), megalospheric form 

 " -V. Lamarcki, d'.Arch." 



.V. variolariiis (Lamk.), microscopic form " .V. lleherti, 

 d'.Vch." 



.V. Orbignyi (Galeolli'). megalospheric form " .V. 

 -.eemmcleiisis, d. 1. H. and v. d. Br., var. elegaiis. Sow." 



In A', laevigatus the microspheric form far exceeds Ihe 

 megalospheric, in the size attained by the full-grown tests, 



t I have here considerably expanded what I take lo be Schaudinn's 

 meaning. His words are (/.<. p. ,,3): "Die Chromidien (of Polyslomella) 

 enlsprrchen den in der Ein- oder .Mehr/'ahl vcrhandenen Gcschlechtskernen 

 Oder Mikroruclei der Ir.fu*oiien. Der I'nterschied besleht nur darin. dass 

 wegen der Verknupfung der Brutbilduu? mil den Kopulationsvorpangen 

 die Geschlechlskemsubstan/ bei Potystoinella in vie! gr'>sseren Quantitiilen 

 vorhanden ist, als bei den Infusorien." 



- "Die Chromidien der I'rotozoen Afclt. /. ry,"--'n,kumle. Ed. v., 

 1 (1904), p. ';«• 



