74 DISCOVERY REPORTS 



Table 4. Szvimbladder dimensions and retial lengths of some bathypelagic and shallozv- 



water teleosts 



and bathypelagic species. The extent of the gas-glands of some of these fishes can be seen in Text- 

 fig- 3 6 - 



While these drawings give a ready impression of the relatively large expanse of the glands in deep- 

 sea species, a more meaningful comparison may be made by estimating the ratio of the surface-area 

 of the gas-gland to the volume of the swimbladder. Measurements were made only on fishes showing 

 good expansion of the gland and swimbladder, the results being given in Table 5. Before considering 

 these figures it should be remembered that the comparison of gas-glands in terms of surface-area is 

 not entirely appropriate, since some are more than one cell in thickness. But as the glands of the 

 three flying fish appear to be no more than one cell thick, this will not bias the figures in favour of the 

 deep-sea species. Of these, Vinciguerria attenuata and probably the two Astronesthes, have single 

 layer gas-glands, while those of Argyropelecus and the three lantern fishes are multi-layered. 



The proportionately greater glandular surface in the bathypelagic species will be immediately 

 obvious. The contrast is as great as that between the two environments. The flying fishes spend most 

 of their life not far below the surface, while the populations of the deep-sea species are centred at 

 various levels between 200 and 1000 m. 



The significance of these differences may be appreciated by comparing the flying-fish, Cypsilurus 

 cyanopterus, with the lantern fish, Myctophum punctatum. A 600-g. Cypsilurus will have a swim- 

 bladder volume of about 30 ml., while the corresponding figure for a 5-g. Myctophum will be 0-25 ml. 

 Assume that the flying fish and lantern fish live at mean pressures of 1-5 and 30 atmospheres re- 

 spectively. Considering the swimbladders only during the steady state, when the gas lost by diffusion 

 is being made up by secretion, we may further assume that the flying-fish loses 5 per cent of the 

 contained gases during the course of a day. The same percentage may be taken for the lantern fish 



