14 DISCOVERY REPORTS 



The gas-gland invests the walls of the sac over a length of about 10 mm. in front of the rete. As 

 the swimbladder was quite relaxed the walls appear to be rather thick. 



Giinther (1887) dissected a Photichthys taken by the 'Challenger' Expedition and described the 

 swimbladder as a ' long simple sac with thick walls '. As already mentioned in the introduction, the 

 ' conical muscular mass ' at the posterior end is clearly the rete mirabile. 



Text-fig. 4. Swimbladder of (a) Gonostoma denudatum (lateral view), and (b, c) G. elongatum (lateral views). In (c) the 

 regressed swimbladder is shown enlarged with part of its investment of fatty tissue, av, artery-vein pair to regressed swim- 

 bladder ; bpr, by-pass branch of retial artery ; //, fatty tissue ; gg, gas-gland ; int, intestine ; k, kidney ; pi and pv, positions of 

 pectoral and pelvic fins ; ra, retial artery ; rv, retial vein ; rm, rete mirabile ; rsb, regressed swimbladder ; st, stomach, (a, x 7-5 ; 

 B, x5- 4 ; c, X15.) 



Ichthyococcus ovatus (Cocco) (Text-fig. 6) 

 St. 1590, 24 10-4' N., 17 18' W., 13. x. 35, TYFB, 400-320 m. Standard length 34 mm. (7-0 x 2-5 mm.). 



While much of the structure could be seen, the swimbladder of this fish was much distorted. 



A single rete (length 2-0 mm.) enters the posterior end of the sac to supply a gas-gland (with one 

 median lobe and two lateral lobes) lying on the floor of the sac. Immediately in front of the gland 



