20S MK, K. PAY 0^ AMinUHlOl $ ANO 



regular wftv of the aorta, some smaller veins coming IVom the 

 trunk likewise to outer into tl»e capillary system of the respira- 

 tory air-sac. 



The ri^spiratory air-sacs are direct continuations of the unicous 

 membrane of the branchial cavity. Two layers enter into the 

 eompositiou of their walls — au external tlbrous, and an internal 

 delicate one. 



HeiN? we see nnich the same process carried out as in the Cuchia 

 eel — blood oxygenated at a respiratory sae, and, conjoined with that 

 oxTgei\ated at the lungs, returned purified direct to the aorta ; 

 whilst an air-bladder (^ii) with its pneumatic duct likewise exists. 



Knowing this, we can now accouut in a most satisfactory man- 

 lier for the experiments and their results. In these amphibious 

 fishes the great proportion of the blood which is oxygenated is 

 thus purified at the respiratory aii'-sac ; this now arterialized 

 bloodj joined with the smaller portion which has been oxygenated 

 at the gills, enters the aorta. In active life and continued mus- 

 cular uvovemeut it is necessary that a large amount of blood should 

 be decarbonized ; in tact the use of the respiratory aii^sacs is re- 

 quired, the access to atmospheric air a necessity. Failing access 

 to atmospheric air, the gills come into play ; and they are able to 

 cai'ry on a moderate amount of oxygenation, but iusntficient for 

 much miiscular action or active exertion. 



Jsow the problem arises. AVhere are amphibious fislies found ? 

 why should they exist ? 



The Labyrinthici are spread throughotxt Sind. India, Ceylon, 

 Burma, Siam, the Malay archipelago to the Philippines, and 

 China. Two genera axe likewise found in Southern Africa. In 

 fact they are distinctly tropical forms, and mostly found in low- 

 lying localities but little removed from tidal reach, or in the deltas 

 of large rivers. 



The Ophiocephalidiv are distributed thonghout the plains of 

 India, Ceylon, Burma. Siam. the Malay archipelago to the Phi- 

 lippines, and China : one species extends westward to Belooeliistan 

 and Afghanistan : and I have taken it at the Andamans. These 

 fishes ai*e very carnivorous ; and I have seen them ptu'sniug the 

 little HajyhcJiiJi up small streams where there would not be suifi- 

 cient water to oxygenate theii* gills ; but respiring atmospheric air, 

 this necessity becomes avoided. Tlie favourite resort of the Ophio- 

 cephalidte is amongst the grass at the margin of a tank, where 

 thev can lie in such shallow water that their mouth is either 



