Species in the case of certain Fishes. 451 



{Tinea vulgaris)^ gudgeons {Gobio Jluviatilis) , spirlins (Albur- 

 nus bij)unctatus) , and minnows [Phoxinus Icevis). The first 

 time we gradually raised the temperature of the water in two 

 hours from 10° to 28° C. (from 50° to 82°-4 F.) ; the second 

 time, in an hour and a half, from 9^° to 27° C. (from 49°' 1 

 to80°-6F.). 



The bullheads, which are without an air-bladder, never 

 ceased to repose upon the gravel at the bottom j but after the 

 temperature had been raised 6°-8° C. (10°-8-14°-4 F.), the 

 perch, with their closed air-bladder, began to depart a little 

 from the bottom, where they had at first remained nearly mo- 

 tionless. At the first moment the warming of the water gave 

 rise to great agitation ; but, the first surprise passed, quiet was 

 restored, and we could then see all the fishes, except the bull- 

 head, struggle with their fins to prevent their being carried 

 towards the surface. As soon as the organs of motion were 

 in repose, the animal rose more or less rapidly, like a balloon, 

 without, however, appearing externally to be in the least 

 inflated or deformed. The Cyprinidas, furnished with an air- 

 bladder having an external communication, ascended and 

 descended alternately; and it seemed to me that the young- 

 struggled with more difiiculty than the adults*. Some adult 

 tench and a gudgeon in particular appeared much less influ- 

 enced than some little tench, which were constantly being 

 forced up towards the surface. At 22° C. ( = 71°-6 F.) one 

 perch (from 7 to 10 centims., or from 3 to 4 inches long) 

 kept about midwater in the aquarium ; at 25° or 26° C. (77° 

 or 78°*8 F.) they went willingly very near the surface ; finally 

 the head, being less elevated, was often turned more or less 

 downwards. At 27° or 28° C. ( = 80°-6 or 82°-4 F.) the agi- 

 tation again became general ; several fishes appeared ready to 

 perish ; and we stopped the experiment, being unable to follow 

 the action of the temperature upon creatures which were, so to 

 speak, stupefied. 



In the first experiment the introduction into the midst of 

 the liquid of a vase of aquatic plants very rapidly restored 

 quietude to the fishes which were agitated by an increasing 

 suffocation. The second time we had fewer made ill, owing 

 to our leaving a plant in the water during the whole expe- 

 riment. 



Although the fish, and especially those in which the air- 



* This would seem to indicate that the capacity and importance of the 

 air-bladder are greater in early youth than in the adult state ; for we 

 know that, in some fishes, the duct of communication with the exterior 

 is rather obliterated with increasing age ; and I have always remarked 

 that the fins are comparatively larger in the young than in the old. 



