v.] IN THE THEORY OF NATURAL SELECTION. 269 



far as we understand the details of their functions, and so far 

 as their structure differs from that of the corresponding organs 

 in other MammaHa — have also been directly or indirectly modi- 

 fied by adaptation to an aquatic life ? Thus all whales possess 

 a very peculiar arrangement of the nasal passages and larynx, 

 enabling them to breathe and swallow at the same time : the 

 lungs are of enormous length, and thus cause the animal to 

 assume a horizontal position in the water without the exercise 

 of muscular effort : in consequence of this latter modification, 

 the diaphragm extends in a nearly horizontal direction : there 

 are moreover certain arrangements in the vascular system 

 which enable the animal to remain under water for a con- 

 siderable time, and so on. 



And now, in reference to this special example, I will repeat 

 the question which I have asked before : — ' If everything that 

 is characteristic of a group of animals depends upon adaptation, 

 what remains to be explained by the operation of an internal 

 developmental force ? ' What remains of a whale when we 

 have taken away its adaptive characters ? We are compelled 

 to reply that nothing remains except the general plan of mam- 

 mahan organization, which existed previously in the mammalian 

 ancestors of the Cetacea. But if everything which stamps these 

 animals as whales has arisen by adaptation, it follows that the 

 internal developmental force cannot have had any share in the 

 origin of this group. 



And yet this very force is said to be the main factor in the 

 transformation of species, and Nageli unhesitatingly asserts that 

 both the animal and vegetable kingdoms would have become 

 very much as they now are, if there had been no adaptation to 

 new conditions, and no such thing as competition in the struggle 

 for existence ^. 



But even if we admit that such an assumption affords some 

 explanation, instead of being the renunciation of all attempts at 

 explanation ; if we admit that an organism, the characteristic 

 peculiarities of which entirely depend upon adaptation, has 

 been formed by an internal developmental force ; we should 

 still be unable to explain how it happens that such an organism, 

 suited to certain conditions of life, and unable to exist under 

 other conditions, appeared at that very place on the earth's 



^ 1. c, pp. 117, 286. 



