66 
structure. It leaves the organ in which it is formed in a simi- 
lar fashion and enters the organic chamber prepared for its 
reception in the same way, the conditions of its development 
being im all respects the same. It has not yet been possible 
(and only 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 ex- 
hibited 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 comparable 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 comparison of the figures with those 
on page 63. 
Fig. 15.—A. Human ovum a ee a. germinal vesicle. >. germinal 
spot. 
B. A very early condition’ of Man, with yelk-sac, allantois and amnion 
(original). . 
C. A more advanced stage (after Kolliker), compare fig. 14, C. 
Indeed, it is very long before the body of the young human 
bemg can be readily discriminated from that of the young 
