SURVEY OF STRUCTURE 



4i 



Gymnoscopelus nicholsi (Gilbert) (Text-fig. 23) 



St. WS 213, 49°22'S., 6o°io'W., 30 v. 28, N 4-T, 249-259 m. B.M. Reg. no. 1948.5. 14. 621-6. Standard 

 length 50 mm. 



The swimbladder, which is found over the middle region of the stomach, measured no more than 

 2-5 mm. in length. As in all myctophids, three retia mirabilia, which are closely bound together, 

 enter the anterior end of the swimbladder. The gas-gland is oval in outline and invests the floor of the 

 swimbladder over its anterior half. The walls of the bladder are so thick that little remains of the inner 

 cavity. Clearly, the organ has undergone considerable regression. 



B 



Text-fig. 23. Swimbladder of Gymnoscopelus nicholsi (a) seen in position in body-cavity, and (b) ventral view. 

 gg, gas-gland; int, intestine; k, kidney; rm, rete mirabile; sb, swimbladder; st, stomach, (a, x 12; B, x 22-5). 



Ceratoscopelus townsendi (Eigenmann & Eigenmann) 



St. 703, io° 59-3' N., 27°03-8'W., 17. x. 31, TYFB, 358-0 m. B.M. Reg. no. 1948.5. 14. 584-5. Standard 

 length 55-0 mm. (5-5 x 1-5 mm.). 



Being in a rather relaxed condition, the swimbladder of this fish did not extend beyond the pyloric 

 end of the stomach. The three retia mirabilia enter the floor of the sac at its forward end to supply a 

 gas-gland that extends from one extremity to the other. However, when the sac is expanded con- 

 ditions may well be different. 



Opposite the point of entry of the retia is the oval, which has the appearance of a collapsed blister. 

 The capillary network is fed through a vessel from the retial artery, while the return circulation is by 

 way of a large vein running upwards to the roof of the body-cavity. 



