SLEEP. XIX 



Does sleep or a periodical season of repose for the organs of the senses, 

 ever visit fish, or can it be that balmy slumber is to them unknown, is 

 a question we occasionally see broached. Hybernation during the winter 

 ' months in cold latitudes, and aestivation during hot months in tropical 

 climates, is generally admitted, but not so simple sleep. Some authors 

 appear to hold to the view that, possessing no eyelids, fish are unable to 

 sufficiently shut out external influences, and cannot therefore bo supposed 

 to sleep. Mammals and birds, in short, are sometimes asserted to be the 

 only animals which are periodically visited by refreshing slumbers, while 

 such as are in a lower grade merely rest from time to time in their labours, 

 and withdraw themselves to some quiet nook where they may remain 

 undisturbed. If all fishes sleep it may be asked how do sharks, dolphins, 

 black fishes and pilot fishes follow ships long distances during many days 

 and nights ? On the other hand, if not sleeping, what are the basking 

 sharks and sun-fishes about, which permit the fishermen to get so close as to 

 drive harpoons into their bodies before they attempt to get away, or the pike 

 in fresh water that allows a noose to be slipped around its head? 



Some years since Mr. Hughes gave an interesting account of how 

 he visited a rock pool at Tenby by candle-light, and noticed several small 

 fishes at the bottom, among them being the active and artful blennies and 

 rocklings. They lay perfectly still, not attempting to dart away to a quiet 

 corner, and permitted the hand to be introduced, when one by one all were 

 caught. These fish seemed either temporarily paralyzed by the light or so 

 sound asleep that their capture was effected with ease. 



In rapid waters it has been suggested whether if fish sleep they use their 

 fins in order to keep their position while in a state of somnolence. In the 

 tanks of an aquarium I was able to observe a small ' ' golden tench " lying- 

 in a peculiar and apparently uncomfortable position ; its tail half was sup- 

 ported by a piece of raised rockwork, while its head was resting on the floor 

 of the tank, and the slightest amount possible of motion only conveyed to 

 the mind of an observer that he was gazing at anything but a dead 

 specimen. The succeeding evening I revisited the tench, and perceived the 

 little golden one as vigorous as its companions, all of which, with a single 

 exception, appeared to be leisurely enjoying their existence, either by 

 feeding or in the contemplation of the varied scenes which were constantly 

 passing in front of their glass enclosure. The solitary exception was 

 reclining on its back and scarcely moved, but on a closer scrutiny its mouth 

 could be seen to open every now and then, and the fish gave a short gasp ; 

 the next evening it was swimming about with its fellow-captives and busy 

 wallowing in the soft sand, some of which it took into its mouth and then 

 discharged again, and a third tench was now in a somnolent state. 



In another tank in the same Institution wrasses could be seen sleeping in 



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