160 HYPOTHESIS OF THE DEVELOPMENT OF 



in some of the series of beings, present us with animals com- 

 paratively high in some respects, to be followed by species in 

 which, owing to the adaptive process, some of the higher 

 features were reduced or erased. It is very curious that this 

 recession of animals at their maturity to a lower range of 

 qualities and an inferior mode of existence, and this recession 

 of animals in the geological series (for example, the coining of 

 saurians without distinct teeth, after the thecodonts which pos- 

 sessed that feature), have been presented together as objections 

 to the theory of Progressive Development, without its being 

 seen that the one fact suggests an explanation of the other, 

 making out a support, instead of establishing a difficulty, for 

 that view of the history of animated nature. 



Early in this century, M. Lamarck, one of the most distin- 

 guished of modern naturalists, suggested that the gradation of 

 animals depended upon some general law which it was impor- 

 tant for us to discover. So far he was right ; but the theory 

 which he consequently formed with regard to the causes of the 

 varieties of animated being, was so far from being adequate to 

 account for the facts, that it has had scarcely a single adherent. 

 What M. Lamarck chiefly grounded upon was the well-known 

 physiological fact, that use or exercise strengthens and enlarges 

 an organ, while disuse equally atrophies it. He conceived that, 

 an animal being brought into new circumstances, and called 

 upon to accommodate itself to these, the exertions which it 

 consequently made to that effect caused the rise of new parts ; 

 on the contrary, when new circumstances left certain existing 

 parts unused, these parts gradually ceased to exist. Some- 

 thing analogous was, he thought, produced in vegetables, by 

 changes in their nutrition, in their absorption and transpiration, 

 and in the quantity of caloric, light, air, and moisture which 

 they received. This principle, with time, he deemed sufficient 

 to have produced the advance from the monad to the mammal. 

 His illustrations were chiefly of the following nature. The 

 bird which is attracted to the water by the necessity of seek- 

 ing there its food, wishes to move about on the surface of the 

 flood, and for this purpose strikes out its toes. Through the 

 consequent repeated separations of the toes, the skin uniting 

 them at the roots is extended, and at length becomes webbed. 

 In like manner, the shore-bird which has no desire to swim, 

 but has to approach the water for food, is constantly subject 

 to sink in the mud. The bird, disliking this, exerts all its 

 efforts to lengthen its legs ; the result is, that, by continual 



