490 SCIENCE PROGRESS. 



We must infer from these facts that the Amphibian larva 

 only resembles the ancestor so far as the conditions of its 

 life resemble those of the ancestor, and differs so far as its 

 conditions of life are different from those of the ancestor. 

 Selectionists of course will see nothing in this inconsistent 

 with their views of modification. They will say that the 

 larva and the adult have varied independently and the 

 fittest have survived in each case. But in this as in many 

 other cases it is important to notice that we have no 

 evidence that the required variations ever occurred except 

 when the conditions of life changed. The mere statement 

 that the modifications occurred and survived because they 

 were advantageous is not sufficient. Supposing that the 

 modifications occurred in certain individuals while all the 

 rest died, then we ask how and why did they occur in those 

 individuals. So long as we regard the Individual as a single 

 definite form like a house or a vase, it may appear conceiv- 

 able that the modifications of individuals are due to changes 

 arising in the germ cell, to blastogenic variations, and that 

 the adaptation of individual to conditions of life is due to 

 the selection among a host of slightly different individuals 

 of those which most approach the suitable structure. But 

 when, as in the case of the frog, we see the same individual 

 always passing in development through two quite distinct 

 stages of life, which are adapted to two incompatible condi- 

 tions, aquatic and terrestrial, we find it much more difficult 

 to form a conception of the mode in which such a meta- 

 morphosis could have been brought about by blastogenic 

 variations. Supposing it to be possible by always breeding 

 from the individuals with the smallest limbs to produce a 

 race or species without limbs at all, it does not follow that 

 it is possible to produce by selection a race in which there 

 are no limbs during the first half of life, and well-developed 

 limbs in the second half. But this is what we have in the 

 frog. It may be said that the two stages are so marked 

 and distinct as to vary independently as though they were 

 separate races, and therefore a different standard of selection 

 can be applied to each. But this simply means what the 

 Lamarckian contends for, namely, that the modifications are 



