28 SUPPLEMENT ON 



the whole nature of the animals to which it is applicable, can 

 in some measure be deduced from it. Being vertebrated 

 they must possess an internal skeleton ; brain and spinal 

 marrow inclosed within the vertebral column ; muscles on the 

 outside of the bones ; they must have four extremities only ; 

 the organs of the first four of the senses in the cavities of the 

 head, &c. As aquatical beings, that is as residents in a 

 liquid more ponderous and obstruent than air, their locomo- 

 tive organs required to be disposed for progression : to ascend 

 being readily obtained, their structure became necessarily 

 subservient to the forms which would cause least resistance 

 forward ; hence their tails received the principal muscular 

 power, and the members were left short, but expansible and 

 furnished with membranes to support them ; and their tegu- 

 ments were made smooth or scaly, and totally free from hairs 

 or feathers. 



As they breathe through the intervention of water alone, 

 that is, as they restore to their blood its arterial qualities by 

 means of the oxygen contained in the air which is suspended 

 in water, the blood is naturally cold ; and their vitality, the 

 energy of their senses and of their movements is consequently 

 less than in mammalia and birds. Thus, their brain, although 

 it be similarly composed, is proportionably much smaller, 

 and the external organs of the senses are not of a nature to 

 impress it with powerful excitements 1 . Of all vertebrated 

 animals, fish, in fact, show the least signs of sensibility. 

 Having no elastic air to act upon, they are destitute, or 

 nearly destitute of voice, and of all the sensations which that 

 faculty awakens or supports. Their immoveable eyes, their 

 fixed osseous face, their members without inflections, moving 

 by totality, have no play in their physiognomy ; no expres- 



1 The brain of fishes appears to have an embryonic character when 

 compared with that of warm-blooded animals, and to have its greatest 

 development in the cerebellum, the seat of the appetites. 



