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Show ON CIJASSIFICA'l'ION. 111 mbrano. I do not wish to strain tho analogy too far, out it is, at any rate, interesting to observe thi ~lose Inorphological resemblance between one of tho lowest of animals and that fonn in which all the higher animals cmnn1once thoh· existence. It is a very remarkable characteristic of this group, that thm·o is no separation of tho Lody into distinct layer~, or into cellular elements. The Gregartt:nida aro devoid of nwutlm and of dige~:Jtivo apparatus, living entirely by in1bibition of the juices Fi~. I. Fig. 1.-A, Gre,r;arinrt of the cnrthworm (after Lieberkiihn ) ; B, eueyste<l; C, I>, wiih the contents uivitlcd into pseudo-navicellm; E, F, free p::;eudo-navicelke ; C:, II, fi ·cc amoobiform content~ of the lattel'. of the anin1al in whose intestine, or body cavity, they arc contained. The most conspicuous of those phenomena, which we ordinarily regard as signs of lifo, which they '.,/hibit, i a certain contraction and expansion along different dimnetors, the body slowly narrowing, and then lengthening, in various directions. Under certain circu}nstances (though the conditions of tho ehango are not thoroughly understood), it is observed that ono of those Gre,r;a.t·inida, whatever its fonn nwy Lo, will convert it~elf into n. well-rounded sae, the outer nw1nLruuo ceasiJlg to exhibjt GltEOAHINIOA, lUll:t.OPOD .. \ ,'PONGIDA, AND I l!'tT JUA. any long<\r those lllOVOlnent. of which I polre, and Leeon1ing coated Ly a strnetnr Jes invo 't1nont, or "cyst" (Fig. 1, D). Tho ub ·tance of tho botly contained within tho cy ·t n xt undergoes a , ·in gular chango. The central nucl n and th • vosiele disappear; after a tin1e, tho Ina~-Js Lr aks up into a sori ~ of rounded portions and, then, each of those rounded portion elongates, and, beroming lightly point cl at each nd, eonstitutt\ s a little body whieJ1 has Loon called a ' Pse'tulo-navicella," fron1 its res01nblanco to the Diatonuteeous Ncwicnla or Navicella (Fig. 1, C, D). N oxt, the cap ·ulo burst~ and th Pse7~clonavicellw (Fig. 1, E, F) aro seatterod and passed ont of tho bo<ly of the auimal which they inhabit. Though, of emu c, a groat nn1nbor of the1n aro dct!troy d, t:l011H', at any rate, aro devoured by other animal~:J; and, when that is tho ca. , the little partide of protein substance· which is inclo cd within the I>seudo-navicella i~ set free frmn its , ·hell, aHd 0xlt.iLits nn1eh 1noro lively Inovontonts than before, thrusting ont proce8ses in various direction~, and drawing thc1u in again, and, in fnct, clm~oly rcsmnbling ono of those aninwJenles wltieh have beC'n call('d Ama?bte (Fig. 1, JI). rrho young A1nrolJifor1n G1·e,r;a'f'ina grow~, increases in izo, and at length assnn1cs tho stnwtur' which it had at fir t. That, in subRtan(' , is all that we know of this lowest division of anhnal life. But it will L(\ obsorvocl, thPre iH a hiatn · in our knowledo·e. \Vo cannot say tlwt we know the whole nature and 1nodo of cxistC'ne of thi~, or any other anin1al, until wo have tracocl it to its exnal state ; but., at pr sout, w know nothing whatever of this <'ondition muong tho Grega1·inw; so that in reasoning aLont th01n wo nn1st always ox rei e a ecrtain retieenco, not knowing how far wo 1nay have to 1nodify our opinions by tho discovery of tho , ·ox1utl state horoaft r. 'rho proee. ·s of becoming encysted, preceded or accompanied very often Ly the n1utual apposition of two GregariHm, was l<n·nlerly inutgined to eorre pond with what is t nnccl among plants "eonjugation."-a proce s which in some eases, at any rat , appears to bo of a , 'C'Xnnl nature. JJnt tho diHc·ovcry that a ~ingle Grega1·ina 1nay Locon1o encysted and Lrcak 111' into P~ewlo-navicellw seoins to nogati v ihi~ aualoo·y. But 11ow, lt•avi11g this, I pa :-; on to Ow Hext <'las~ i lmt wltieh |
