over, proceed gradually, continuously, and without any interrup- 

 tion of active life. The larva having started into independent 

 existence as a fish, does not relapse into the passive torpor of the 

 ovum to leave the organizing energies to complete their work un- 

 troubled by the play of the parts they are to transmute, but step 

 by step each organ is modified, and the behavior of the animal 

 and its life-sphere are the consequence, not the cause, of the 

 changes." 



"The external gills are not dried and shrivelled by exposure to 

 the air, nor does the larva gain its lungs by efforts to change its 

 element and inhale a now respiratory medium. The beak is shed, 

 the jaws and tongue are developed, and the gut shortened, before 

 the young Frog is in a condition to catch a single fly. The em- 

 bryo acquires the breathing and locomotive organs — gills and com- 

 pressed tail— while imprisoned in tbe ovum ; and the tadpole ob- 

 tains its luiiLTs and land-limbs while a denizen of the pool ; action 

 and reaction between the germ and the gelatinous atmosphere of 

 the yolk, or between the larva and its aqueous atmosphere, have 

 no part in these transmutations. The Batrachian is compelled to 

 a new sphere of life by antecedent obliterations, absorptions and 

 developments, in which external influences and internal efforts 

 have no share." 



While the passage we have quoted is an attack against La- 

 marckianism, we do not see but that in a long course of genera- 

 tions of the ancestors of the present species of amphibians, the 

 metamorphoses may have become gradually established, finally be- 

 coming the normal history of each individual ; the changes of the 

 individual epitomizing the successive steps in the collective life- 

 history of the entire group of Amphibians. That changes in the 

 physical surroundings induce important modification of structure 

 is seen in the exceptional mode of metamorphosis of the Surinam 

 Pipa, or the Hyla of Mauritius, and on the other hand, in the 

 prematurity of the axolotl, which near the level of the sea drops 

 its gills, while five or six thousand feet above the sea it retains its 



To' recapitulate, we have the following stages of development 

 in the Amphibia : 



1. Morula (segmentation total). 



2. The embryo develops as in the bony fishes. 



3. Young with external gills hatching with a fish-like form, but 



