178 ZOOLOGICAL PHILOSOPHY 



grasping objects, these unused legs have entirely disappeared, in- 

 cluding their bones, and even the pelvis which served for their support 

 and attachment. 



The degeneration in the Umbs of cetaceans under the influence of 

 the environment and acquired habit is also seen in their fore-feet, 

 which are entirely invested by skin so as not even to show the digits 

 at the end of them ; they thus consist of one fin on each side contain- 

 ing the skeleton of a concealed hand. 



Seeing that the cetaceans are mammals, it is assuredly a part of 

 their plan of organisation to have four limbs Uke all the rest, and 

 consequently a pelvis for the support of their hind-legs. But, here as 

 elsewhere, the loss of these parts is the result of an abortion due to a 

 long disuse of them. When we remember that in seals which still 

 have a pelvis, this pelvis is impoverished, reduced and does not pro- 

 trude from their haunches, we shall feel that the cause must be the 

 moderate use which these animals make of their hind-legs, and that, 

 if they were to give up using them altogether, the hind-legs and even 

 the pelvis would ultimately disappear. 



The arguments which I have just adduced will doubtless seem to be 

 mere guesses, since it is not possible to establish them on direct 

 positive proofs. If we pay attention, however, to the observations 

 set forth in the present work, and if we then closely examine the 

 animals which I have cited and also the effects of their habits and 

 environment, we shall find as a result of this examination that these 

 guesses acquire a high degree of probability. 



The table on p. 179 may facilitate the understanding of what I 

 have said. It is there shown that in my opinion the animal scale 

 begins by at least two separate branches, and that as it proceeds it 

 appears to terminate in several twigs in certain places. 



This series of animals begins with two branches, where the most 

 imperfect animals are found ; the first animals therefore of each of 

 these branches derive existence only through direct or spontaneous 

 generation. 



There is one strong reason that prevents us from recognising the 

 successive changes by which known animals have been diversified 

 and been brought to the condition in which we observe them ; it is 

 this, that we can never witness these changes. Since we see only the 

 finished work and never see it in course of execution, we are naturally 

 prone to believe that things have always been as we see them rather 

 than that they have gradually developed. 



Throughout the changes which nature is incessantly producing in 

 every part without exception, she still remains always the same in her 

 totaUty and her laws ; such changes as do not need a period much 



