CHAP. IV. MOTIONS OP FISHES. Ill 



had alive, in our possession, at different times, always 

 raised the hody in a semi-perpendicular position, by 

 grasping hold of some object, before they took to flight; 

 while their motion, or walk, upon a level surface, so 

 far from exhibiting any degree of " despatch," was re- 

 markably slow; and they seemed to move their legs in 

 a forward direction with the same sense of pain as is 

 experienced by the sloth, under similar circumstances. 

 Bats have another peculiarity, alike unknown among 

 other animals, excepting a genus of birds (Colius). 

 When at rest, either during the day, or the period of 

 hybernation, they suspend themselves, with their heads 

 downwards. If we consider the general construction 

 of these animals, it appears highly probable that this is 

 the position they always assume, in a state of nature, 

 previous to the opening of their wings for the purpose 

 of flight : the wings, in fact, being part of the fore legs, 

 are thus as free as those of a bird, and are ready for 

 instant expansion, without having first to loosen their 

 hold of any substance. 



(132.) Almost the only motion of fishes is that of 

 swimming ; and this has been justly said to be nearly 

 the same kind of action in water, as flying is the air. 

 Same of the organs employed for this purpose resemble, 

 in their mode of action, the oars of a boat, particularly 

 the pectoral and the ventral fins, while the tail, in its 

 office, and even in its shape, may be termed the rudder. 

 The exact use of the dorsal and anal fins has not been 

 clearly ascertained. They would seem intended chiefly 

 to preserve the fish in a perpendicular position, as well 

 as to cut the water, both above and below, to facilitate 

 the progress of the fish and they may, probably, per- 

 form both these purposes : and yet it has been ob- 

 served by Mr. Yarrell, that some fish, from which he 

 removed the dorsal fin, and placed afterwards in water, 

 did not appear to feel any sudden injury from the de- 

 privation. The muscular force of the tail is very 

 great, and acts like the handle of the rudder. It is 

 astonishing with what velocity some of the larger fish 



