264 



ZOOLOGt. 



a little capping to a large hollow bladder (blastodermic 

 vesicle). This capping represents the blastoderm proper, 

 and from it alone is the embryo developed. The general 



r e s e m - 

 blance of 

 this stage 

 to the early 

 stage of the 

 fowl's ovum 

 is striking, 

 if we regard 

 the secreted 

 fluid as re- 

 placing the 

 yolk. 



From this 

 point on- 

 ward, the 

 develop- 

 ment fol- 

 lows that 

 of the chick 

 in all broad 

 general 

 features. 

 Primitive 

 streak, neu- 

 ral folds, 

 notochord, 



mesoblastic somites, amnion, etc., all appear in practically 

 the same way as in the chick. The only important differ- 

 ences concern the extra-embryonic structures. 



6. Yolk-Sac Placenta. The yolk-sac of the rabbit 

 (often called the umbilical vesicle) never contains yolk, but 

 at a very early stage of development, when the ovum has 

 passed along the fallopian tube and entered the uterus, the 

 yolk-sac grows out towards the wall of the uterus. It is 

 of course separated from the actual wall of the uterus, first 

 by the false amnion or serous membrane (cf. fig. 135), and 



Fig. 189. SEGMENTATION OF RABBIT'S OVUM 

 (From Balfour, after Van Beneden.) 



