: NT OF TIN-; TWO MIDDLE C.l.\i\\ I 



11 



the choidal fundament as a single layer, become two layers thick 

 farther down, and thus meri:e into the. more voluminous accumu- 

 lation of yolk-celK, which, in all Amphibian emhryo>, occupy tin* 

 ventral Mde and reM riot the gast rula ca\ it y. They correspond, to 

 continue with our comparison, with the entalerm, whereas the 

 small-celled mattes, which. Martini: I'rom the fundament of tin- 

 chorda, have crowded themselves out between the entodcrm and 

 the outer -fnii layer, are comparable with the cells which in Am- 

 phioxus and in our diagram form the wall of the h> I the 



middle germ-layer. The 



conclusion is t h-i et'ore jus- '' 



tided and very obvious, 



that in Triton the two mid- 



' rtA /' 



/// ///' <i iit''rir territory of 

 tin' i:iiil>i-inniic body b;i 



'$8 oj evagination at 

 l>ntli sili'x of the chordal 



lament, just as in Am 

 //// ./-//x, t <<<' pt that in on-e 

 case the evayinated cell-mass 



tins <r ('//////, in the 

 (>(//>'/ case none. 



A cross xrtion through 

 (he blastopore of the Triton 

 embryo (ti-'. 7S) is to be 



;>un>d \\ith our second 

 diagram (fig. 75). The 



hollow hodv .xai-s of the latter corropond to the solid cell hands, 

 which are the fundament of the middle germ-layer. Near 

 hlaMopore (u) they are split into two lamellae. Of these the outer 

 (////,') nieru r e>. a> in our diagram, into the inner layer of the bi 

 joric lip, and becomes continuous at the edge of the blastopore with 

 the outer -eriu-layer (.//) ; the inner lamella (ink*), on the cont 



'iinec-ted with the iua>s of yolk-cells (</:. which lies like a wall in 

 front of the blastopore and even projects into it as the lit s< UNI AN 

 yolk-plug (dp). 



roM.-riorly t.. the blastopore, the middle germ 

 out for >oine distance, hut here only a> a Millie connected n . 



According to the region from which the middle g.-rm-laycr is de- 

 veloped, wt may divide it into t\\o j ,:id call that part which 



ift 



_ dh 



Fig. 78. Cross section through the blastopore of an 

 egg of Triton with feebly expressed medullary 

 groove. 



ale, Outer, <X-, inia-r gt-rni-l.iy.T ; int 1 , parietal, mi-*, 



nil laniflhi of the nii.HU- -.-i in-hiver ; u, 



\.ilkcells; dp t yolk-plug; dh, 



intcstiii.-il i-;ivity. 



