II DEVELOPMENT OF MAN 91 



by some rare chance can it ever be possible) to 

 study the human ovum in so early a developmental 

 stage as that of yelk division, but there is every 

 reason to conclude that the changes it undergoes 

 are identical with those exhibited by the ova of 

 other vertebrated animals ; for the formative 

 materials of which the rudimentary human body 

 is composed, in the earliest conditions in which it 

 has been observed, are the same as those of other 

 animals. Some of these earliest stages are figured 

 below and, as will be seen, they are strictly com- 

 parable to the very early states of the Dog ; the 

 marvellous correspondence between the two which 

 is kept up, even for some time, as development 

 advances, becoming apparent by the simple com- 

 parison of the figures with those on page 86. 



Indeed, it is very long before the body of the 

 young human being can be readily discriminated 

 from that of the young puppy ; but, at a tolerably 

 early period, the two become distinguishable by 

 the different form of their adjuncts, the yelk-sac 

 and the allantois. The former, in the Dog, becomes 

 long and spindle-shaped, while in Man it remains 

 spherical: the latter, in the Dog, attains an 

 extremely large size, and the vascular processes 

 which are developed from it and eventually give 

 rise to the formation of the placenta (taking root, 

 as it were, in the parental organism, so as to draw 

 nourishment therefrom, as the root of a tree 

 extracts it from the soil) are arranged in an en- 



