28 DISCOVERY REPORTS 



Two blood-vessels enter the anterior end of the sac and then subdivide to form about twelve 

 branches, which take more or less parallel courses within the swimbladder wall until they reach the 

 gas-gland. Each of these vascular branches consists of from six to twelve closely associated capil- 

 laries, which are arranged in the form of a ribbon. In cross-section the ribbon consists of alternating 

 arterial and venous capillaries (or arterioles and venules), the arterial elements having a diameter of 

 about i2(i while the venous ones measure about 20 fi. Clearly these are retial structures (see Text- 

 fig. 14D), but they are quite unlike the massive retia of most teleosts with a closed swimbladder. Such 

 elements might well be called micro-retia mirabilia. 



These retia enter the gas-gland without subdividing and form capillary loops within the secretory 

 tissue. The gland occupies a median region and entirely surrounds the sac. Beyond the gas-gland the 

 walls consist of an inner epithelium and outer connective tissues. Perhaps it is here that resorption 

 of gases takes place. 



Opisthoproctus grimaldii Zugmayer (Text-fig. 14 e) 



St. 1746, from 32 02-1' S., 87 02-5' E. to 31 56-6' S., 86° 55-1' E., 22. iv. 36, D.R.R. 2513 m. Standard length 

 65 mm. (15-0 x 6-o mm.). 



Opisthoproctus grimaldii has a capacious swimbladder which is rounded anteriorly and tapers to a 

 point at the other extremity. As in O. soleatus, blood-vessels enter the forward tip of the sac. There is 

 a large vein that originates between the kidneys (presumably coming from the cardinal vein), while 

 there are two arteries, one being a branch of the mesenteric system, the other running forward from 

 the vessel to the ovaries. 



Again, these vessels subdivide to form micro-retia, each composed of a ribbon of closely associated 

 capillaries (from twelve to sixteen). The venous elements have a diameter of from 12 to ibfi, while 

 their arterial counterparts measure from 8 to io//. At the forepart of the swimbladder there appeared 

 to be about 30 micro-retia, these running backward to supply glandular patches, which seemed to be 

 less concentrated than those of O. soleatus. However, they were most numerous over the middle part 

 of the sac. These patches are formed of cells varying in size from about 30 to 150^. 



Winteria telescopa Brauer (Text-fig. 14 A, b) 

 St. 2066, 04 56-4' N., 14 467' W., 5. v. 37, N 450 B, 1550-0 m. Standard length 100 mm. (5-0 x 2-0 mm.). 



The swimbladder of Winteria is suspended in the body-cavity just behind the stomach. In the 

 above individual the sac is very relaxed, the walls being thick and having a nacreous appearance. 

 From the posterior end of the swimbladder a long band of connective tissue runs backwards to an 

 attachment on the right ovary. 



An artery and vein enter the anterior end of the sac and subdivide into a number of smaller vessels, 

 which run towards the gas-gland. This is found in the posterior half of the sac and seems to be a 

 flattened oval structure lying on the floor of the swimbladder. However, the tissues are so shrunken 

 that this may not be its true form. Running to the glandular area are at least twelve micro-retia 

 composed of from eight to fourteen capillaries. 



Macropinna microstoma Chapman 

 Chapman (19426) was unable to find a swimbladder in this species. 



Family Microstomidae 

 Xenophthalmichthys danae Regan 

 Bertelsen (1958) records that the swimbladder is absent. 



