8o DISCOVERY REPORTS 



In Winteria and Opisthoproctus the swimbladder does not appear to be differentiated into two 

 sharply demarcated sections. The micro-retia and gas-gland are certainly found in the anterior part 

 of the sac, but behind this the walls seem just as thick. Perhaps the capillary system is found in the 

 rear part of the sac, but I was unable to ascertain this in the material at my disposal. 



Text-fig. 38. Swimbladder of Argyropelecus aculeatus, (a) with the resorbent capillary network expanded and the gas-glands 

 contracted, (b) with the capillary network relaxed and the gas-glands expanded, en, capillary network; gg, gas-gland. 



Order Iniomi, Suborder Myctophoidea 



Myctophidae. The resorbent surface of the lantern fish swimbladder is an ' oval ' like that found in 

 various gadoid, macrourid and spiny-finned fishes. It is a thin-walled circular part of the swimbladder 

 and is surrounded by radial and circular smooth muscle fibres, having an antagonistic action. When 

 the radial fibres contract (the circular ones being relaxed), the oval with its rich supply of capillaries 

 is stretched and exposed to the gases in the swimbladder. The circular muscles act as a sphincter. 

 As they contract the thick-walled parts of the swimbladder wall surrounding the oval are drawn 

 towards its centre, eventually coming together. As the oval shuts, its walls are thrown into ridges and 

 folds, and at the end of the process it looks like a wrinkled projection on the face of the sac. 



In most of the myctophids I dissected, the oval had this appearance. It was fairly well expanded 

 in two specimens of Myctophum punctatum and one of Diaphus dofleini, and half-open in a specimen 

 of D. rafinesquei and of Lampanyctus guentheri. It has already been suggested that the structure 

 Rauther (1922) described in Diaphus rafinesquei as the praevesica is actually an oval, and the same is 

 presumably true of the conical projection found at the front end of the swimbladder of Lampadena 

 chavesi (see pp. 38-39). 



A longitudinal section of a closed oval in Myctophum punctatum is shown in PI. III. At high 

 magnifications the circular and radial muscles could be seen, the former having a ' bunched-up ' 

 appearance. The inner epithelium, close to which lies the capillary network, is thrown into folds, 

 while the tissues in the walls have relaxed during the closure. No doubt this accommodation is made 

 possible by the semi-gelatinous nature of the submucosa, although in the oval of the perch (Perca 

 fluviatilis) Saupe (1939) found the gelatinous and fibrous components to be much reduced. 



The myctophid oval lies at the anterior end of the swimbladder close to the retia mirabilia (see 



