306 THE DEVELOPMENT 



;>/' <<>it> c/i l ylps^ si chpshdam 1 



si v l v p$ ch ql t> 2 si 



Fig. 207. 

 206. 



In this profile figure (fig. 206) it is the thin strip (eA, c/t 1 ) which 

 is split away from the subsidiary layer, (si,) except at its anterior 

 (ch) and posterior (ch 1 } ends, and in the transverse section (fig. 

 207) it appears as the small circle (ch) which immediately under- 

 lies the primitive stripe, (ps,) and is flanked right and left by a 

 thick layer, (v,) likewise split off from the subsidiary layer, 

 which thins out to a sharp edge (j; 1 , v~) near the margin of the 

 disc. With these additions and the further development of the 

 parts already begun we have the following characters, namely, 

 the infiltrating albumen (al l ) occupying the whole upper half of 

 the egg; the germinal layer, not only depressed so as to form a 

 furrow all around the germinal disc, but its fold bent inward (at 

 am } , am s ) and elevated so as to partially overlap the slightly in- 

 curved and sunken head (hd) and tail and sides, as it were, 

 enclosing the embryo in a sort of socket, the beginning of a 

 development of the amniotic sac; the head (hd) considerably 

 increased in thickness, or depth ; the primitive stripe (ps, ps^) 



Fig. 206. The same as figs. 204, 205, still more advanced. 2 diam. y, the 

 yolk ; y l , surface of y ; at 1 , the clear, albuminous space ; gl, the germinal disc ; 

 hd, the head ; ps,psi, the primitive stripe ; ch, ch 1 , the chorda dorsalis ; am 1 , am 3 , 

 the peripheric fold of the amniotic sac : 7?i 2 , the space beneath am 1 , and closed 

 below by sfi; si, sl l , sl~, the subsidiary layer. Original. 



Fig. 207. A transverse section of the body, and the layers immediately about 

 it, of fig. 206. a/ 1 , the clear, albuminous space; ps, the primitive stripe; gt, the 

 germinal layer of the disc; ch, the chorda dursalis ; v, the vertebral layer; v 1 , 

 i a , the edges of v ; am', the peripheric fold of the amniotic sac ; am 2 , the space 

 beneath the fold of am 1 ; .s7, nl, si-, the subsidiary layer. Original. 



