SURVEY OF STRUCTURE 13 



Before continuing this survey, certain generalizations may be introduced at this stage. By doing 

 so the descriptions can be more readily followed and needless repetition avoided. 



We have seen that the swimbladders of the foregoing species of gonostomatid fishes have certain 

 common features. These are: (1) a single, bipolar rete mirabile, which is formed at the posterior end 

 of the sac, and (2) a resorbent capillary system that obtains its arterial supply through a by-pass 

 branch of the retial artery. These characters are also shared by other stomiatoid fishes with a well- 

 formed swimbladder in the adult phase. Furthermore, the first feature, at least, can be traced in 

 adults with a regressed swimbladder. In the following descriptions, unless otherwise stated, the 

 lengths of the major and minor axes of the sac are given in parenthesis after the standard length of 

 the fish. 



Gonostoma denudatum Rafinesque (Text-fig. 4 a) 



B.M. Reg. no. 85.6.22. 73-6. Messina. Standard length 81 mm. (16-0 x 2-0 mm.) 



The swimbladder is elongated and fits close beneath the kidneys, extending down some two-thirds 

 of the length of the body cavity. It originates above the bases of the pectoral fins and ends over the 

 pelvics. Reference to Text-fig. 4 a will show the close reciprocal relations between the shapes of the 

 swimbladder and kidneys. 



The bipolar rete mirabile, which is club-shaped and about 2-5 mm. in length, runs straight into the 

 posterior end of the swimbladder floor. It is formed from two vessels running down through the 

 kidneys from the dorsal aorta and the cardinal vein. The gas-gland invests most of the swimbladder 

 floor and also extends over the lateral walls of the wider, posterior part of the sac. 



Just before its point of entry, the retial artery gives off the by-pass branch to the capillary system. 

 Although not traced, this system must be formed immediately in front of the more extensive, posterior 

 part of the gas-gland. 



Gonostoma elongatum Giinther (Text-fig. 4B, c) 



St. 285, 2 43' 30" S., oo° 56' 30" W., 16. viii. 27, i25-i75(-o) m. B.M. Reg. no. 1930.1.12. 74-7. Standard 

 length 149 mm. 



At first sight the swimbladder appears to be completely absent in this species. In place of the long 

 gas-filled sac found in G. denudatum is a long rod-like mass formed of golden-yellow fat globules 

 suspended in a reticulum of connective tissue cells. At the posterior end of this rod the fatty tissue 

 extends over a small cream-coloured body that receives an artery and vein running down through the 

 posterior enlarged part of the kidneys (see Text-fig. 4c). These vessels are clearly homologous with 

 those forming the rete mirabile in G. denudatum. In fact, the creamy-coloured tissues to which they 

 lead are the remnants of the gas-gland and rete mirabile. 



Gonostoma bathyphilum Vaillant 

 No trace of a swimbladder could be found in this species, not even in a fairly young fish (standard 

 length 77-5 mm.) from St. 3094, 44 20' N., 16 49' W., 21. v. 54, TYFH, isoo(-o) m. 



Photichthys argenteus Hutton (Text-fig. 5) 



St. 101, 33° 50' to 34 13' S., 16 04' to 15° 49' E., 15. x. 26, N 450 H, 3SO-40o(-o) m. Standard length 141 mm. 

 (4-5 x 2-0 mm.). 



The swimbladder of Photichthys is unusual in form. The sac is a long tube originating over the 

 stomach and extending down about three-quarters of the length of the body-cavity. 



At the posterior end is an ellipsoidal bipolar rete mirabile, which is rather more than 3 mm in length 

 and about 1-5 mm. in middle depth. The capillaries of the rete are formed by two vessels coming 

 from the dorsal aorta and cardinal vein (between the kidneys). 



