MIGEATORT PrSHES OF ASIA. 211 



bladder as described, with its pneumatic duct leading to tbe ali- 

 mentary canal — and its supply of blood being arterial wben re- 

 ceived, venous as returned into the general circulation. But we 

 have also the respiratory air-sacs, which are direct continuations of 

 the mucous membrane of the branchial cavity, and consequently in 

 the embryonic state were connected with the upper extremity of 

 the alimentary canal. That this respiratory air-sac with a lung- 

 like formation is, as a rule, absent in fishes, is no argument against 

 this view ; for the swim-bladder is likewise often absent. This 

 respiratory air-sac, when existing, appears to be always in con- 

 nexion with the alimentary canal, the swim-bladder only some- 

 times, whilst the latter has also communication with the acoustic 

 apparatus. Lastly this respiratory air-sac receives venous and 

 returns arterial blood into the general circulation. 



The SaccohrancTius, in short, is a true amphibious fish, with 

 both a respiratory sac and swim-bladder, the former of which has 

 an analogous function with, and is, I believe, the homologue of, 

 the respiratory sac of amphibians ; whereas its swim-bladder, 

 which cannot also be the homologue of the same organ, both 

 existing in the same species, I leave for future consideration. 



Having thus briefly reviewed the amphibious fishes of India 

 and the East, we arrive at the question of the migrations of Indian 

 fishes. Before commencing this, a few explanatory remarks are 

 necessary. Thus marine fish very frequently migrate into the fresh 

 waters for breeding or predaceous purposes. Sometimes passing 

 over high banks with a flood tide, their return to the sea is frus- 

 trated by the waters falling; and it not uncommonly happens 

 that fish thus made prisoners of cannot reenter the sea until the 

 succeeding year. Many doubtless die ; some do not ; in fact, Hyder 

 in the last century introduced the Ghmios salmoneus from the sea 

 into a tank in Canara, and they are there to this day. On the 

 other hand, did one ever hear of a freshwater fish retiring to the 

 ocean to breed ? one has been said to have been captured out at 

 sea. I allude to the Gohius giuris. I do not question the fact ; 

 but I suppose the reason to have been as follows. During the 

 monsoon-season great volumes of water are carried down the 

 rivers, dry watercourses become impetuous torrents, rivers are 

 so full that nothing withstands their current. I have seen hill- 

 snakes washed down in Malabar, even so far as Cochin ; and at 

 one of these periods I obtained a bottle of fresh water taken some 

 miles out at sea, but opposite the opening of the Cochin river. 



