24 METAMORPHOSES OF MAN 



in size, and fills those portions of the chorion which 

 are not occupied by the allantoi's. 



Thus, in Hermella and Teredo, the entire egg, 

 including the envelope, is converted directly into a 

 real animal. In mammalia, on the other hand, an 

 embryo, consisting of a few elements, whose final 

 condition will alone reveal their real nature, shows 

 itself upon an almost imperceptible portion of the 

 germ, and becomes more and more isolated. The 

 germ itself contributes directly to the development 

 of the new being only in the earlier stages of its 

 formation. After the egg becomes attached to the 

 uterus, and possibly before that period, it draws all 

 its nutritive supplies from external sources, and the 

 envelopes are the parts which play this important 

 function intermediate between the mother and her 

 offspring. 



Indeed, there are not always such very considerable 

 differences between vertebrata and invertebrata. In 

 frogs, for example, not only is the egg separated 

 from the mother, and consequently charged with the 

 nutrition of the embryo, but even the germ itself 

 encroached on rapidly by the skin, organizes, so to 

 speak, layer after layer, and at the moment of its 

 final transformations seems as though it had been 

 directly formed; so much so, that some naturalists 

 appear to think that it really is thus formed. On 

 the other hand, Weber and Grube, two German 

 naturalists, have described, in the leech and clepsine, 

 phenomena recalling in many ways those which take 

 place in mammalia. 



However, it does not appear that in Annulosa, 

 Mollusca, or Coelenterata, there is a true germinal 



