156 LECTURE VI. 



son witli the stages of development in a land animal — than the 

 pectoral fins ; and their small proportional size reminds the homo- 

 logist of the later appearance of the hind limbs, in the development 

 of the land Vertebrate. But the hind limbs more immediately relate 

 to the support and progression of an animal on dry land than the 

 fore limbs : the legs are the sole terrestrial locomotive organs in 

 Birds, whose fore-limbs are exclusively modified, as wings, for motion 

 in another element. The legs are the sole organ of support and pro- 

 gression in Man, whose pectoral members or arms are liberated from 

 that office, and made entirely subservient to the varied purposes to 

 which an inventive faculty and an intelligent will would apply them. 

 To what purpose, then, encumber a creature, always floating in a 

 medium of nearly the same specific gravity as itself, with hind limbs ? 

 They could be of no use : nay, to creatures that can only attain their 

 prey, or escape their enemy, by vigorous alternate strokes of the hind 

 part of the trunk, the attachment there of long flexible limbs would 

 be a grievous hindrance, a very monstrosity. So, therefore, we find 

 the All-wise Creator has restricted the development and connections 

 of the hind limbs of Fishes to the dimensions and to the form which, 

 whilst suited to the limited functions they are capable of in this class, 

 would prevent their interfering with the action of more important 

 parts of the locomotive machinery. 



In most fishes the ventral fins merely combine with the pectoral 

 fins in raising, and in preventing as outriggers, the rolling of the 

 body ; but some very interesting modifications of the ventral fins, in 

 relation to particular habits of certain species, may be noticed. In 

 the Blennies, the Forked Hake {Phycis), the Forked Beard (Bani- 

 ceps), and some other fishes, the ventral fins are reduced to filamentary 

 feelers. In the Lump-suckers {Cyclopterus), the ventrals unite to- 

 gether, and combine with part of the pectorals to form a sucking disc 

 or organ of adhesion, below the head, just as the opercular and 

 branchiostegal fins are united together to form the gill-cover. In 

 the long-bodied and small-headed abdominal fishes, the ventrals are 

 situated near the anus, where they best subserve the office of ac- 

 cessory balancers ; in the large-headed thoracic and jugular fishes, the 

 loose suspension of these fins, and the absence of any connection with 

 a sacral part of the vertebral column, permits their ti'ansference 

 forwards, to aid the pectoral fins in raising tlie head. 



The following short account of some experiments upon fish, made 

 for the purpose of ascertaining the use of their fins, I give in the 

 words of their gifted describer, Paley, to whom Comparative Physio- 

 logy owes many beautiful accessions to its teleological applications. 

 "In most fish, beside the great fin — tlie tail, we find two pairs of 



