i,i;\ r.i.Mi-MiiM "i mi: fWO MIMM.I: QBRM-LAl 135 



like the one >t' the Kabbit hen- Bgored to be mi-taken for it. In 

 the CftSe of tin- human iiilr\>. (me > 'iii^ primitive 



groove. :u ..1 at tli.- easily recognisable blastoporic lip (///) tin- bend- 

 ing ovt r of tin- outer & rm lay. r (//) into tin- pari* tal lam. lla (//Jt 1 ). 

 The viM-eral lamella (////t 2 ) is well -|>arat .1 t'n 111 th- latter fm- some 

 di.Mahc : ui l r tin- primitive groove it is merged with the inn. -r 

 germ-layer, tlu-Ml^es of the potential fold> ..f tin- two >ii.-s being 

 fu-i (1 int.) a ma-> of oils, which forms the floor of the primitive 

 groove. 



Kinallv an agreement with the development <>f tin- Amplni-i.- 

 not wanting in sections which are made through the ( mln-yonic 

 areas of Birds, Reptiles, and Mammals W< /'/*'/ the primitive groove. 

 The middle germ-layer begins to spr al its-lf out back wan 1 

 not, lio\ve\.r. as in the antt rior part of the emhryonic ana, in 

 the form of paired fundaments, but rather as a single continuous 

 cell -ma^s. This outgrowth too is united to the two primary 

 germ-layers only in the region of the posterior end of the primi- 

 tive streak, being elsewhere distinctly separated from both of 

 them. 



For the completion of the previous account, some statements 

 about the further growth of the middle germ 'ay. r may now be 

 a.l.ltd, cone* rninir which cross sections through inhryos of \arious 

 afford evidence. The middle germ layer >pna.N it>. If out 

 on all sid,s between the two primary germ-lay. r>, farth. r and 

 farther from the place of its first formation the vicinity of the 

 primitive groove. At first it is limittd to the fundament of the 

 embryo itself, then it makes its way into the area pi-llucid:i. ai.d. 

 finally, it is encountered in the opaque area. Everywhere and 

 antly in its extension it appears as an entirely independent 

 layer, at least two cells thick, which i> Be] a rated from its surround- 

 i>y lissuiv>. It is found to be united for a short distance with 

 the inner and outer germ-layr>. but only at the primitive gr 

 which p; r>i>ts for a long time, in old. r embryos even, as we have 

 alnady learn, d from >urf ace -views. Even in the >tage when the 

 nenrenterk: canal traverses the primitive >tnak. and put-, the 

 ceolenteric cavity (under the entoderm, fig. 100 7/y) in communication 

 with the n.-ural tube, we see the cellular lining of the canal and the 

 middle germ-lay, r fused, so that in this region a connection >till 

 exists between all three germinal layers. Compare the accompany- 

 ing cross sections through embryos of Lao-rtu muralis. 



After the statement of the actual conditions, the <ju >tins remain 



