GAR-PIKES, OLD AND YOUNG, 191 



It is so recently that all structural differences and changes were 

 supposed to be readily explicable upon the doctrine of final causes, 

 that we naturally turn first in that direction. Some transformations 

 certainly seem to relate very distinctly to the welfare of the individ- 

 ual, as when the caterpillar becomes a butterfly, and when the aquatic 

 larvas of mosquito and dragon-fly change their forms with their hab- 

 its and modes of life. So, among the vertebrates, it is obvious that 

 the tadpole is by no means adapted to the necessities of the frog and 

 the toad ; and the intermediate stages, resulting from the gradual loss 

 of the tail and the acquisition of legs, while perhaps not particularly 

 suited to either aquatic or terrestrial locomotion, seem to be required 

 in order to permit the development of the lungs and the accompany- 

 ing disappearance of the gills. 



But can the transformations of the gar-pike's tail be thus accounted 

 for ? According to present knowledge and justifiable inference, the 

 Lepidosteus not only passes the whole of its life in the water, but is 

 also, from first to last, an active, predaceous fish, requiring all pos- 

 sible advantages of form and fin in order to overtake its prey. 



Since no marked change occurs in the general form of the body, 

 we may perhaps assume that it is perfectly well adapted to the fish's 

 needs ; although this suggests the general inquiry as to the cui bono 

 of the almost infinite variations from the ideal form supposed to be 

 best suited to aquatic locomotion. 



But do we know, or can we easily infer, any differences in the ne- 

 cessities or the manner of life of the Lepidosteus at different ages, 

 which may account for its having a tail first like a lamprey's, then 

 like a sturgeon's, and, finally, like that oi Amiaf 



It may be suggested that the rapid and, at most, invisible vibra- 

 tions of the filament enable the young gar to glide stealthily upon its 

 prey. But the very young would seem to be even more in need of 

 such precaution, and with them the tail is relatively as large as in 

 the adult, although differently shaped. Finally, even if we conclude 

 that the three distinct stages of the tail are perfectly adapted to cer- 

 tain hypothetically unlike necessities, what shall be said of the inter- 

 mediate conditions? While growing, the infra-caudal lobe must be 

 rather a hinderance than a help to the movements of the primitive 

 tail; and while disappearing, the filament, being useless, must be, if 

 anything, an incumbrance. 



Shall we, then, conclude that these changes in the appearance of a 

 single individual are for the sake of variety as some would explain 

 the great diversity of specific form and coloration among animals and 

 plants ? 



At the present day, neither of the explanations above given is like- 

 ly to wholly satisfy the large class of thinkers who, whether or not 

 they accept any particular evolution doctrine, are inclined to believe 

 that there is, in many cases, a more or less exact parallelism between 



