DETELOPMEIN'T OF THE CHICK FIRST PERIOD- 



299 



c, area 



area presents a pyriform outline (figs. 327 and 328). Under 

 the canal for the spinal 

 cord, which is bounded by 

 the dorsal laminae, we ob- 

 serve the chorda dorsalis 

 the dorsal cord (figs. 330 

 and 332, A, e, and fig. 

 331, /), an extremely fine 

 elongated streak, surround- 

 ed by a transparent sheath ; 

 both the dorsal cord and 

 the sheath go to constitute 

 the cartilaginous column 

 which appears later, and out 

 of which, by its becoming 

 divided into pieces, the ver- 3 27.-Yolk of the natural size 



tebral column is produced after eighteen hours of incubation : a. 

 (466). The embryo with vitellus ; b, area pellucida; 

 its laminae dorsales now vasculosa. 

 bends itself forward, at the 

 same time that it here forms 

 a sickle-shaped transparent 

 fold (fig. 328, c), the future 

 involucrum capitis the 

 cranial envelope or cap. 

 From the twentieth to the 

 twenty-fourth hour, the 

 transparent germinal area 

 is observed to become 

 longer and more fiddle- 

 shaped. The cristae, or 



folds of the dorsal laminae, 



i ,1 i Fig. 328. The pellucid area of 



where they run closest to- | 27 magnified; \ the peUucid 



gether, appear somewhat area? now become pear-shaped ; in- 



siimously bent (fig. 331, stead of the nota, or primary streak, 



b,b} ; here, too, inthepecto- the two dorsal laminae or folds (lami- 



ral region, on both sides of n " s - P Kc<e dorsales) b, b, are seen ; 



... i i the involucrum capitis, or cranial en- 



the dorsal laminae, near velope? c> a faldfo ^ fold| or kind of 



their cnstEe, there appear reflex blastoderma, begins to be de- 

 dark, four-cornered looking veloped. 



