212 THE DOCTRINE OF DESCENT. 
the acquisition of this peculiarity by the necessity of. 
adaptation. If the mode of life of the marsupial frog, 
which carries its young in a membranous fold of the 
back, and the Surinam toad, of which the larve live 
singly in the chambers of a kind of honeycomb on the 
back, were better known than they are, we should 
assuredly arrive at the same results as with the black 
salamander. In the absence of other knowledge, the 
observations of M. Bavey, Marine Pharmaceutist at 
Guadaloupe, first published in 1873, are of the highest 
importance.” A frog of those parts (Hylodon Martini- 
censis) goes through its whole metamorphosis in the 
egg. In the egg it has gills and tail; and from the brief 
remark that the island contains only rapid running 
streams, and nowhere stagnant waters or marshes, it 
appears that this is also a case in which adaptation 
modifies and curtails development. 
If, after tris introduction, we now examine the so- 
called direct development with more attention, it may 
in every way be compared to the metamorphosis of 
the Hylodes of Guadaloupe. Direct development is 
a transformation in the ovum; and in the cases in 
which it occurs, the phases of embryonic development 
are repetitions, more or less distinct, of the historic 
development of the family. We will only particularize 
in the embryonic life of the Vertebrata (in which 
metamorphosis does not take place), some phases that 
are stages of curtailed transformation, and recapitu- 
late the permanent condition of their progenitors. It 
has been repeatedly mentioned that in all vertebrate 
animals, the vertebral column is first laid out as an 
unsegmented cord and an unsegmented sheath for the 
