MATUHA'IIOX OF THE EGG. i] KS8 OF FIM.H 33 



niich'olus, :ind not Separated l'i-in the j M.I. pla-m l.y :my 

 similar di>tinction> in tin- .-i.ndifii.n ot the ^<-rmii 

 !e and tin- C.L'.I: nucleus nrur t hiMu<_'h"iit tin- animal kingdom. 

 'I'ln- I'm -iiiation "f polar cells and tho accompanying motamorpl 

 of tin* ^ermina'ive vehicle into such an ext raonlinarily i'cdiu--d egg- 

 nticlfU-. is It plii'noiiu'n"n of \MV \\ide. j.roliahly, indcrd, <t' _i:Mj-r:i 1 



nviKv. Polar cdl> have been observed throughout tin- rn-im- 



ti-raies, Kchinoderms, NVonns, and Molluscs. In th- rip.-nini: of th.- 



i-opods. acconlin.ir to lli.> .-arli.-r ol.M-rvat ion>, tli.-y 



;i]i tared m-vi-r to be present; but recently tl been lound in 





Fig. 14. Mature egg of an Ichinoderm. It em- loses in the yolk the v try so; all homogeneous 

 Fig. 15. Immature egg from the ovary of an Echinodern?, 



mimerou.- .-pecies by a number of observers, especially by BLOCHMANN 

 and WKISMANX. Among V rti'brate- polar cells are always en- 

 countend in Cyclostomes and Mammals, \vherea> in Kishe> and 

 Amphibia they have been identified only in some cases, ami in Keptile- 

 anl I'.hds not at all as yet. They arise either some time before or 

 elM- diirini: fertilisation. 



In the case "f Mammals t Ilabbit ami Mouse) the process has ' 

 very carefully investigated by VAN HI:NEDKN. and recently byTAiAM. 



... uc-k- before the ruptuiv of the (JIIAATIAN follicle the 

 minative vesicl- a>cends to the Mirface of the egg; some days before 

 that epoch it there di>app:-a rs, and at the p!ac.- wlu-re it di-app. 

 there are formed the egg-nodeufl and, under the /.ona pellucida, one 

 or two ^TAKAXI) polar cells. T . r it has escaped from the 



L>\ary always exhibit.- e^-- nm-leus and polar cells. 



Also in the case of Pishes, Amphibia, Reptiles, and Birds, whose 



3 



