SURVEY OF STRUCTURE 9 



tissue investing the floor and lateral walls of the sac (Text-fig. ia-c). The forward, mid-ventral edge 

 of the gland lies about half-way along the length of the swimbladder. The median part runs across 

 the sac, while the lateral sections extend backwards and upwards to end just below the pigmented 

 roof. 



The rete mirabile is bipolar 1 in structure. It is formed from an artery and vein which break up into 

 several thousand closely intercalated capillaries, these running parallel courses along the length of 

 the organ. At the forward end they recombine into arteries and veins which supply the gas-gland. 

 Two lateral artery-vein pairs enter the gland behind and just below its two upper edges, while there 

 is a mid-ventral association of a vein with two flanking arteries. The vein runs forward to a point 

 about half-way between the rete and gas-gland and then forks before entering the gland. The two 

 arteries closely follow this venous path (see pp. 78-79 for stomiatoid blood circulation). 



Behind the gas-gland there is an extensive capillary network running over the whole of the sac 

 (and just below its inner epithelium). The arterial supply comes from a branch of the retial artery, 

 which forks just before entering the rete. This branch runs forwards along the left side of the rete 

 to a point just in front of it and then gives off a number of sub-branches. In ventral aspect, the 

 vascular pattern may be appreciated by reference to Text-fig. ib. It will be seen that the artery 

 divides into three main sub-branches. Text-fig. ic also shows that one main sub-branch travels to 

 the roof of the sac and there subdivides into arterioles and capillaries. 



The capillary circulation is completed by the three veins to the gas-gland, which give off lateral 

 venules. Those from the mid-ventral vessel and those from the lower sides of the two lateral vessels 

 are associated with the arterioles of the three ventral sub-branches referred to in the last paragraph. 

 The venules from the upper sides of the two lateral vessels divide to form capillaries that join those 

 of the single dorsal arterial sub-branch. 



This capillary circulation forms the resorptive part of the swimbladder, the region where gases 

 diffuse into the blood when deflation of the sac becomes necessary. 



The swimbladder of the smaller (39*5 mm.) fish has a very different appearance although its 

 structure is basically the same. But the comparison of these two swimbladders, coming from fishes 

 taken in the same haul, will best be left to a later section (p. 64-65). 



Vinciguerria nimbaria Jordan & Williams 

 St. 1768, 33 49-8' S., 12 50-8' E., 19. v. 36, N 100 B, 290-i5o(-o) m. Standard length of fish 34 mm. 



The structure of the swimbladder of this species is much like that of V. attenuata. The major and 

 minor axes of the ellipsoidal sac measured 5-5 and 2-0 mm. 



Pollichthys mauli (Poll) (Text-fig. 2A-c) 



St. 273, 9 38' 00" S., 12 42' 30" E., 31. vii. 27, N 100 B, n8(-o) m. B.M. Reg. no. 1930.1.12. 254-9. Standard 

 length 43 mm. 



This species has a capacious, thin-walled swimbladder occupying much of the upper part of the 

 body cavity. The sac is ellipsoidal, the measurements of the major and minor axes in the above fish 

 being 5-0 and 2-2 mm. The posterior part of the organ fits snugly into a recess in the fore part of the 

 enlarged, rear section of the kidneys, while the anterior end lies above the stomach. 



At the posterior extremity of the sac is a single, bulbous rete mirabile (length 1-2 mm.), which 

 supplies a horseshoe shaped gas-gland investing much of the floor and lateral walls of the swimbladder. 

 The gland fits round the rete and encircles an oval-shaped capillary area, which is set in the middle 

 part of the floor. 



1 See also page 69. 



