SURVEY OF STRUCTURE 15 



is part of the resorbent system, which receives two arteries from the by-pass branch of the retial 

 artery. The curious lateral projection of the swimbladder shown in Text-fig. 6 is undoubtedly due to 

 distortion. This is probably the roof of the posterior part of the sac, the part that fits closely within 

 the recess formed by the kidneys. 



This projection contained the other part of the resorbent capillary system, for it is supplied from 

 a third branch of the by-pass artery and receives branches from periglandular veins. However, the 

 full appreciation of the circulatory system must be left until a better preserved specimen is available. 



rv ra 



Text-fig. 5. Swimbladder of Photichthys argenteus (lateral views). Above, general view; below, posterior part of swim- 

 bladder, also showing the appearance of the gas-gland in transverse sections, gg, gas-gland; hit, intestine; pv, origin of 

 pelvic fins; ra, retial artery; rv, retial vein; rm, rete mirabile; st, stomach. (Top figure, X2'4; bottom figure, x 12.) 



Cyclothone Goode & Bean 



In Cyclothone the swimbladder regresses after metamorphosis into the adult form and becomes 

 invested with fat, which is deposited between the tunica externa and peritoneum of the larval organ. 

 As the peritoneum may be regarded as forming the outermost layer of the swimbladder wall (see 

 Fange, 1953), and as, in Cyclothone, it completely surrounds the fat and the regressed tissues, this 

 entire structure will be called a swimbladder in the description that follows. 



Cyclothone signata Garman (Text-fig. 7C-E) 

 Dana St. 7735, 29. vi. 51, 58 20' N., io° 00' W., 1500-m. wire. Standard length 31 mm. 



The swimbladder of this fish lies just in front of the posterior part of the kidney, the backward 

 end reaching a little beyond the points of insertion of the pelvic fins. In side view the organ is 

 elliptical in shape, having a length of about 3 mm. and a median depth of rather less than 1 mm. 

 Except for the postero-ventral part, it is covered with black peritoneum, which also covers a tubular 

 backward extension running under the bulbous terminal segment 1 of the kidney. 



This backward extension contains an artery and vein, which enter the rear part of the swimbladder 

 and then divide into a number of smaller vessels. These are bound together in a long rete mirabile 



1 This is largely formed by the Stannius body (Owen, 1938). 



