Proceedings of the Scientific Meetings of the Zoological Society of London 1874

Page 380

314 MR. G. E. DOBSON ON T H E [May 19, ceased to respire, and lay at the bottom of the vessel. To show that their deaths were not due to a deleterious condition of the water, it was carefully drawn off (a small portion sufficient to cover the fish being allowed to remain) and fresh substituted, without, however, permitting the fish to reach the surface. The fresh water seemed to produce no change in their condition. At 5 P.M. the largest specimen lay on its side; at 7 P.M. all were dead. Both the speci­mens in water with free access to the surface were alive at this hour ; but one died at 10 P.M., probably from wounds it had received ; the other was found dead next morning*. Exp. 3.-A specimen of Saccobranchus singio was placed in the same jar, having the netted diaphragm similarly fixed 1 inch beneath the surface of the water. It made but few attempts to reach the surface, and died in four hours. Another specimen placed in the jar afterwards swam about in a very lively manner, and made several attempts to reach the surface of the water; it died in two hours. The difference in the time required to cause suffocation was pro­bably due to the greater exertions made by the second specimen, which exhausted the supply of air faster. Other specimens kept for observation in m y aquarium with free access to the air were observed, when approaching the surface of the water, to discharge a considerable amount of air from the gill-openings, immediately afterwards placing the muzzle above the water. Exp. 4.-A specimen of Amphipnous cuchia\ was placed in the glass jar, which was more than half filled with fresh water. The netted diaphragm was omitted, in order to observe its mode of respi­ration. The habits of the animal while in the water were noted during eight days, with the following results :-It was found that the fish either lay in a semitorpid state at the bottom or remained sus­pended in the water, keeping its head resting against the side of the jar about 1 inch or less below the surface. The used-up air was expelled from the gill-apertures, at first slowly, one bubble succeeding another till four or five were discharged ; the remaining air was then expelled by a single effort, the fish immediately sinking to the bottom of the jar, most probably as the direct result of suddenly increased specific gravity. Usually in about two minutes afterwards the animal raised itself by muscular effort, placed the muzzle at the surface of the water, separated the lips slightly (precisely as a snake does when * I do not consider the above-described experiment as conclusively proving this species to be a mixed air- and water-breather; for although very many specimens were procured by m e for the purpose of examining their respiration, the greater number died before I could find an opportunity for making the necessary experiments; and even those examined were most probably in a sickly condition, as shown by the death of the other two specimens, not confined beneath the surface of the water, a few hours later. When placed in the aquarium these fish invariably kept swimming round and round, having the extremity of the muzzle at the surface of the water, or remained vertically sus­pended with the mouth at the surface. This seems to m e to indicate that unmixed air was also required for the purpose of respiration. t For a description of the respiratory organs in this fish, see Owen's ' Ana­tomy of Vertebrates,' vol. i. pp. 481 & 487.