THE FISHES. 187 



the caudal fin, the lobes of which are like the blades of 

 a screw. Retrograde motions can be made by fish in an 

 imperfect manner only by forward strokes of the pectoral 

 fins. When the fish wants to turn towards the left he 

 gives a stroke of the tail to the right, the right pectoral 

 acting simultaneously, whilst the left remains adpressed to 

 the body. Thus the pectoral fins assist in the progressive 

 movements of the fish, but rather directing its course than 

 acting as powerful propellers. The chief function of the 

 paired fins is to maintain the balance of the fish in the 

 water, which is always the most unsteady where there is 

 no weight to sink it. When the pectoral of one side or 

 the pectoral and ventral of the same side are removed, the 

 fish loses its balance and falls on the side opposite ; when 

 both pectorals are removed the fish's head sinks ; on re- 

 moval of the dorsal and anal fins the motions of the fish 

 assume a zigzag course. A fish deprived of all fins, as well 

 as a dead fish, floats with the belly upwards, the back being 

 the heavier part of the body " (" Study of Fishes," p. 44). 



As we find that these so-called low order of vertebrates 

 have the power of exercising some of the higher functions 

 of those much further advanced in the scale of creation, 

 and as it is well known that all animals of the higher 

 orders are obliged to have a period of repose for the brain, 

 the question arises, Have fish the power of sleeping ? 



Muller (" Elements of Physiology ") says : " The excite- 

 ment of the organic processes in the brain which attends an 

 active state of mind gradually renders that organ incapable 

 of maintaining the mental action, and thus induces sleep, 

 which is to the brain what bodily fatigue is to other parts 

 of the nervous system. The cessation or remission of 

 mental activity during sleep, in its turn, however, affords 

 an opportunity for the restoration of integrity to the organic 

 conditions of the cerebrum, by which they regain their 

 excitability. The brain, whose action is essential to the 

 manifestation of the mind, obeys in fact the general law 

 which prevails over all organic phenomena that the 

 phenomena of life, being particular states induced in the 

 organic structures, are attended with changes in the con- 



