2IO THE DOCTRINE OF DESCENT. 



shape of their bodies not inconsiderably, and from gill- 

 breathers, and aquatic animals became lung-breathers 

 and terrestrial animals. It needs further observation to 

 ascertain whether (what is, however, very improbable), in 

 their home, all Axolotls, after having propagated them- 

 selves in their larval state, undergo the metamorphosis 

 into salamander-like animals (Amblystoma), or whether 

 the transfer to Europe and the consequent entire change 

 of the circumstances of life gave the impulse to a pro- 

 p-ressive transformation of these few individuals, which, 

 by the continuance of these conditions, would in future 

 o-enerations extend to more and more individuals, and 

 finally become the characteristic of a new species. 



The examples of Ontogenesis, or individual develop- 

 ment, hitherto examined, had the peculiarity that the 

 sexual animal does not issue directly from its egg like 

 the Phoenix from its ashes, but had to pass through 

 various forms and existences in which the progenitors 

 of the species again become alive and palpable. We 

 must now inquire how this development is related to that 

 form of reproduction which the systematizers, completely 

 in accordance with the facts, yet without any corre- 

 sponding meaning, have termed " direct development," 

 or "development without heterogenesis or metamor- 

 phosis } " The ciliated embryos of many Medusae are not 

 converted into polype-like intermediate forms, but pass 

 directly into Medusae. The greater number of higher 

 crabs do not leave the egg as Nauplia, but as more or 

 less perfect decapods. The bird, the mammal, and 

 man are all at birth "similar to their parents." Con- 

 sidering that the processes of heterogenesis are in them- 

 selves by no means advantageous to or " in harmony 



