210 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- 
gressive transformation of these few individuals, which, 
by the continuance of these conditions, would in future 
generations 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 Phcenix 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 Medusz are-not 
converted into polype-like intermediate forms, but pass 
directly into Medusa. 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 
