REPRODUCTION, 69 
Fig. 72.—Various stages in the segmentation of a fowl’s egg (Kiliker). 
ing the primitive hypoblast. After incubation for a couple of 
hours, these cells become differentiated into a lower layer of 
flattened cells (hypodlast), with mesoblastic cells scattered be- 
tween the epiblast and hypoblast. It is noteworthy that, in the 
bird, segmentation will proceed up to a certain stage indepen- 
dently of the advent of the male cell, apparently indicating a 
tendency to parthenogenesis. 
Fic. 73.—Portion of section through an unincubated fowl’s oesper (after Klein). a, epiblast 
composed of a single layer of columnar cells ; b, irregularly disposed lower layer cells of 
the primitive hypoblast ; c. larger formative cells resting on white yelk ; f, archenteron. 
The segmentation cavity lies between a and b, and is nearly obliterated. 
