XX NERVOUS AND TEGUMENTARY SYSTEMS. 



all sorts of curious positions, mostly at night-time, but likewise- occasionally 

 during tbe day, especially soon after they had taken a meal. These after- 

 dinner naps, as well as such as were indulged in at. night-time, appear to 

 be often passed in the same portions of the tank day after day, while the 

 positions assumed by the three-spotted wrasse are by no means less uncom- 

 fortable than such as are seen occurring among the tench. Blennies have 

 been observed to occupy the same bed-rooms night after night, while I can 

 only suppose that the little suckers, Liparis, sleep during the day-time when 

 they hide themselves in order to be able to move about during the night, 

 which appears to be their period of activity, as they then search for food. 



Among the fishes of India which inhabit the fresh waters perhaps the air- 

 breathing snake-headed species gives us the best example of sleeping fish. 

 In the month of December a few years since, while investigating the 

 fisheries of Assam, I was with a party engaged in exploring the Sissera 

 River. We entered a canoe and cautiously ascended the stream. When about 

 three miles from camp all of a sudden our boatmen ceased pulling, and 

 pointed to an object lying in the water under the bank, whispering that it 

 was a large fish fast asleep. We stealthily approached and got within two 

 yards of the spot, when we easily saw a snake-headed morrul, Opliiocephahis, 

 about four feet in length, lying perfectly still and apparently fast asleep, 

 just on the surface of a deep pool in the stream. Our repeating carbine was 

 silently passed to our crack shot, he steadily raised it to his shoulder, took a 

 deliberate aim, fired, but we saw the fish no more. Since then I have 

 frequently seen these fishes in an apparently sleeping condition. 



THIRST. 



Living as these animals do in a watery medium it would appear that the 

 sense of thirst must bo unknown, or else that it is quenched by means of 

 endosmosis through the skin. Were this not the case it is difficult to 

 conceive how the salt water forms could satisfy such a longing. 



TEGUMENTARY SYSTEM. 



The skin or tegumentary system may be entirely or partially scaleless, or 

 should scales be present they may be partially imbedded in the skin, the 

 posterior or external portions of one not overlapping its neighbour, and 

 termed non-imbricated ; or they may overlap each other like tiles, when they 

 are termed imbricate. The powers of resistance against external violence is 

 augmented when hard substances enter into its composition, consequently 

 those fishes which are most liable to injury are defended by scales or plates, 



