DEVELOPMENT OF THE CHICK FIBST PERIOD. .301 



cond day of incubation the embryo disconnects itself even 

 more and more from the ger- 

 minal membrane and the 

 yolk, and rises more dis- 

 tinctly over the germinal 

 area. * This takes place by 

 the anterior plait or fold (l/i- 

 volucrum capitis) continu- 

 ing to recede still farther 

 backwards (fig. 334, e), and 

 the development posteriorly 

 of a second plait or fold, 

 sickle-shaped or crescentic 

 in the first instance also (fig. 

 334, g), the future incolu- 

 cruni caudce; the sides now 

 begin to turn inwards also, 

 by which the transparent 

 germinal area is drawn in 

 and bent laterally, and 

 made to assume a complete 

 fiddle-shape (figs. 333 and 



Fig. 33L-Magnificd view of the 

 lines in length ; the broader pelll f cid ^ of the yolk> fig> 330 . the 



and more strongly bent ex- area has now lost its pear-shape in a 

 tremity, with its transverse great degree, and become somewhat 

 plait or envelope, is visible fiddle-shaped (biscuit-shaped in the 

 n the naked eve The cris- original). In the middle are seen the 



slightly sinuous edges of the dorsal 



tae ot the dorsal laminae lamina> 6> 6> separating from one ano- 

 have become approximated ther anteriorly and posteriorly; on 

 through a larger space, their outsides lie four square plates, 

 touch each other (fig. 334, c > c > rudiments of the vertebral co- 

 6) and finally coalescing %!**?%%& 

 completely, close the canal i ucrura> shining through; /, dorsal 

 for the spinal cord (fig. 335, cord. 

 A, g), beneath which the 



more delicate chorda dorsalis with its sheath (e) extends. The 

 four-cornered laminae, the future vertebral arches, have in- 

 creased in number, new ones springing up in front and be- 

 hind ; and, about the thirty-sixth hour, as many as from ten 



