SURVEY OF STRUCTURE n 



The rete, like that of Vinciguerria, is bipolar. At the forward end is a large median vein which soon 

 forks to send branches round the inner edges of the gas-gland. Each of these two branches is accom- 

 panied by an arterial vessel, an association supplying the anterior parts of the gland. The posterior 

 parts on either side of the rete also receive two artery-vein pairs (see Text-fig. 2). 



The capillary network, through which gas may leave the swimbladder, is fed with arterial blood 

 through a vessel coming from the retial artery. This by-passes the rete and runs forward along the 

 mid-ventral line to give off arterioles that break up into capillaries. The venous part of the circulation 

 comes from the large median vein of the rete. 



Bonapartia pedaliota Goode & Bean (Text-fig. 2D-f) 

 St. 1582, 05° 39-1' S., 46 22-3' E., 29. iv. 35, N 450 H, i900-i8so(-o) m. Standard length 67-0 mm. 



The swimbladder of Bonapartia is a thin-walled, capacious ellipsoidal sac lying immediately in 

 front of the enlarged posterior part of the kidneys. When fully expanded it is likely to occupy more 

 of the body cavity than that shown in Text-fig. 2F. The major and minor axes of the sac measured 

 about io-o and 5-0 mm. 



A large club-shaped rete mirabile (length 3-6 mm.) runs under the posterior part of the swim- 

 bladder floor. Again it is bipolar in structure, supplying the gas-gland through vessels that are formed 

 by the capillaries when they reach the anterior end of the organ. The gland, which is a single structure, 

 fits closely round the rete. Its form may best be appreciated by reference to Text-fig. 2D. 



Immediately in front of the gland, and on the floor of the sac, is an oval-shaped capillary region. 

 As in Pollichthys and Vinciguerria, the arterial part of the circulation is provided by a branch of the 

 retial vessel. The venous part could not be traced in its entirety but seems to arise from two vessels 

 running forward through the gland. (These veins may also provide part of the glandular supply.) 



Maurolicus muelleri (Gmelin) (Text-fig. 3) 

 St. 2072, 46 31-6' N., 07 42-9' W., 22. v. 37, TYFH, i7o(-o) m. Standard length 22 mm. 



As in other gonostomatids, the swimbladder of Maurolicus lies forward of the posterior part of the 

 kidneys. The major and minor axes of the ellipsoidal sac spanned 4-5 and 2-0 mm. The walls were 

 quite thin, having a thickness of between 10 and 20//. 



A single rete mirabile (length 075 mm.) is found at the posterior end of the sac and is formed by 

 an artery from the dorsal aorta and a vein from the cardinal vessel (between the kidneys). 



The gas-gland is four-lobed. Two smaller, rounded lobes lie above and to the side of the front part 

 of the rete. The two larger lobes are oval in shape and extend over the floor and side walls of the 

 middle section of the swimbladder. The long axes of these two lobes are parallel to that of the sac 

 and measure 1-4 and 1-5 mm., the left being the larger. Each lobe receives a closely associated 

 artery-vein pair emerging from the front of the rete, which is thus bipolar in structure. 



There is a fine-meshed network of capillaries (the resorbent surface) lying just below the inner 

 epithelium of the sac and between the lobes of the gas-gland. The median ventral area between the 

 two larger lobes extends forward beyond their anterior ends, while the two lateral areas between the 

 small and larger lobes extend upwards over the side walls of the sac. The arterial supply to the 

 capillary network comes from a branch of the retial artery, which runs forward under and beyond the 

 rete to a point close in front of its distal end, where it divides into three sub-branches. Two of these 

 run outwards, each between the corresponding small and large lobe of the gas-gland. The third sub- 

 branch proceeds forward along the mid-ventral line between the two large glandular lobes. These 

 three vessels give off lateral arterioles, which break up into capillaries. The four veins to the gas- 

 gland lobes complete the capillary circulation, each vein sending off branches that partly encircle the 



