Fig. 324. The same vitellus, but 

 with a piece of the vitellary membrane 

 and the subjacent blastoderma re- 

 moved at a, by which the nucleus of 

 the cicatriculae, or cumulus proligerus, 

 a dark disciform substance implanted 

 in the vitellus, is brought into view. 



DEYELOPMEXT OF THE CHICK FTEST PERIOD. 29 i 



portion of the blastoderma 

 is called theareavitellina. 

 About this period also the 

 separation of the blasto- 

 derma, in the direction 

 of its thickness, becomes 

 more apparent; between 

 the serous layer, which 

 still continues limited to 

 the germinal area, and 

 the mucous layer, which 

 extends into the vitelline 

 area, there appears a 

 new lamina, which, how- 

 ever, is only distinctly 

 denned towards the pe- 

 riphery, where it ap- 

 proaches the limits of 

 the area vasculosa ; in 

 the direction of the thick- 

 ness this lamina lies in 

 the blastoderma as if it 

 belonged to both of the 

 other layers, and pene- 

 trated into their sub- 

 stance ; to distinguish 

 this less separated lami- 

 na, it ia spoken of as the 

 'far lamina, the 

 blood and blood-vessels 

 first making their ap- 

 pearance within its sub- 

 stance. This formation 

 first becomes distinctly 

 visible between the six- 

 teenth and twentieth hour 

 of incubation (fig. 329, 



25. Magnified view of the portion of the blastoderma removed 

 in fig. 319. a, the nota, or primary streak ; 6, the oblong area pellucida ; 

 c, the oval area vasculosa. 



