354 Miscellaneous. CHAP. xxv. 



animation, while in animals such as the hare and the weasel its lightness 

 has passed into proverbs. But passing from the sleep of birds and mammals 

 we find that many insects have periods of torpid seclusion connected with 

 the varying requirements of their conditions of life ; and even plants sleep, 

 closing their petals at night, erecting and folding together their leaves, the 

 sensitive plant losing its sensitiveness, and plants, generally, exhaling at 

 night a different gas from what they exhale by day. 



" If, then, sleep obtains in such endless variety of degree and purpose in 

 such a multitude of forms of animal and plant life within our knowledge, 

 does it not raise the presumption that it may well obtain also, in many more 

 ways not yet within our knowledge ; is not the\ presumption rather in 

 favour of sleep in some manner being a general rule rather than an excep- 

 tion? And in the case of fish we have the still further presumption in 

 favour of their having the power of sleeping, by the known fact, instanced 

 above, of some of them sleeping the sleep of aestivation. As to hybernation, 

 also, we know that the ova of the salmonidae are ordinarily influenced by it 

 every year in nature, and can, by its aid, be kept in a state of suspended 

 animation for lengthened periods, at the will of man, when under transport 

 to the Antipodes. We have also read of fish frozen as stiff as sticks reviving 

 under warmth, but I do not know how much reliance may be placed on the 

 accuracy of such statements. On the whole, therefore, there would seem to 

 be nothing improbable in the idea of fish enjoying times of suspended 

 energies of the nature of sleep. 



" It may be argued per contra that the character of the element in which 

 fish live precludes sleep, in that they must keep on exercising their muscles 

 to maintain their position. But even in a stream positions can be, and are, 

 chosen by fish in which the necessity for movement is reduced to a minimum 

 as, for instance, behind a large stone, under a protruding bank, or among 

 roots. And it is not necessary to sleep that the cessation of muscular 

 action should be complete, only that it should be reduced so as to give 

 repose. Birds, for instance, and some horses, sleep standing, and birds 

 exercise other muscles to keep the head under the wing, and even man con- 

 tinues to exercise the muscles of his eyelids to close them and keep them 

 closed, and the muscles of his respiratory and blood-circulating organs, only 

 in a less degree than when not asleep. It is a matter of degree, varying 

 with the needs of the system in case. 



- " For myself, I incline to the belief that the needs of fish likely to induce 

 sleep are probably connected with temperature, as indicated above, and 

 with food, for it is noticeable that fish can endure prolonged fasts, during 

 which they remain inactive, and that they are per contra endowed with the 

 most rapid digestions, so as to allow of their recuperating the system in 

 marvellously brief periods. Their rate of growth is so much more regulated 

 by food than by anything else that, reasoning from analogy, it is a natural 

 conclusion that the presence of exceptional powers of digestion and growth, 

 under exceptional feeding, argue the probability of the converse obtaining 



