S I '.i .TIT. ; wo MNHH.K CKUM -\.\\ I.I,-. 



(If ///// diio </< Bird* and Rqritfe*, A-' ///- 



' N /'<//? i/K'ntioH. This margin exhibits i vrry different relation-hip 

 1'ri'in that of the primitive Stria k or hla<topore ; it is a | culiarity of 

 lnerohlaMii- eggB, which is uu>t int in;at -ly aociatd with tin- origin 

 partial Cleavage, It indie-alts tin- place at which tip- s.-gm-nt. (1 

 portion of tin- grim miets tin- niiM'.L'mented portion the place at 

 which there li- in llir yilk frrc nuclt i, liy in ans nf wliicli a supjilr- 

 m-ntary clra\a^.- is k-pt up until !a!-- Ma^i-s in thr jtroccss of 

 Ifv.'lnpinciit. until, in fact, the time when the two primary :_ 



rs have been formed by means of the in valuation whioh 

 i rur> at iln- Ma^topore. At the expense of the cell-mat i-rial. whii-h 

 is constantly lu-ing augmented by supplementary cleavage, the germ- 

 layns iiHTcasr in cxtt-nt at their place of transition into the yolk, 

 and thus gradually grow over the imsegmented part. W/iereas at 

 tlif Llnstopore an invagination of cells <i?rt>/</ present takes place, there 

 ensues at the margin of the germ-disc a formation of new cells, and 

 thereby an increase of the marginal part and an overgrowth of the 

 ylk. I tin rt fore propose for it the name circumcrescence-ma /'//// 

 f tin' yolk-sphere. There can be no such thing as a separate openini: 

 *! a yolk-blastopore, because the yolk is an organic part of the germ. 



ami is in continuity 

 with the segmented 

 part of it by means 

 of the layer whii-h 

 contains the yolk- 

 nuclei. 



If we would insti- 

 tute a comparison be- 

 t\\ i'ii animals with 

 meroblastic eggs and 

 theAinphiliiaat a stage 

 when gastnilation is 

 not yet completed, then 

 the blastopore of the 

 Amphiliia. which is 

 indicated by the letter 

 u in the accompany 

 section through the 



-a>trula of a Triton (fig. 102), corresponds to the prostoma of Rep- 

 tiles, and to the crescentic and primitive grooves of Birds; the still 

 t.\] osed mass of yolk-cells corresponds to the yolk-material which is 



Fig 102. -~ Longitudinal section through a gatrula of Triton. 

 r, i, inner germ-layer ;//,, ck-ava-e-cavity ; 

 1 on ; u, blastoiwre ; rfz, yolk-i-- 

 ventral lip of the cit-Icn-- 



