212 THE DOCTRINE OF DESCENT. 



of life of the marsupial frog, which carries its young 

 in a membranous fold of the back, and the Surinam 

 toad, of which the larvae 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, 

 Alarine Pharmaceutist at Guadaloupe, first published in 

 1873, are of the highest importance."" A irog of those 

 parts (Hylodon Martinicensis) goes through its whole 

 metamorphosis in the egg. In the egg it has gills and 

 tail; and from the brief remark that the island con- 

 tains only rapid running streams, and nowhere stag- 

 nant waters or marshes, it appears that this is also 

 a case in which adaptation modifies and curtails devel- 

 opment. 



If, after this 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 trans- 

 formation in the ovum; and in the cases in which it oc-- 

 curs, the phases of embryonic development are repeti- 

 tions, more or less distinct, of the historic development 

 of the family. We will only particularize in the embry- 

 onic life of the Vertebrata (in which metamorphosis does 

 not take place), some phases that are stages of curtailed 

 transformation, and recapitulate the permanent condi- 

 tion of their progenitors. It has been repeatedly men- 

 tioned that in all vertebrate animals, the vertebral column 

 is first laid out as an unsegmented cord and an unseg- 

 mented sheath for the spinal cord. This is the permanent 

 state of the lower fishes. In the higher Vertebrata also, 



