SURVEY OF STRUCTURE 23 



side of the rete mirabile, which is undoubtedly homologous with the artery forming part of the 

 capillary network in other stomiatoids. Sections also reveal that there is a capillary network on the 

 floor of the sac between the lobes of the gas-gland and there also appears to be another network 

 in the roof. 



Family Astronesthidae 

 Astronesthes niger Richardson (Text-fig. 11) 

 Dana St. 1378 111 , 200-m. wire. B.M. Reg. no. 1929. 1.4. 93. Standard length 41 mm. (5-5 X2>5 mm.). 



The swimbladder of this fish, which is elliptical in profile and has thin walls, is slung above the 

 stomach, the extremities lying over the origins of the pectoral and pelvic fins. 



A rod-like rete mirabile (1-5 mm. in length) enters the posterior part of the sac. Its blood supply 

 comes from an artery that runs backwards and then upwards between the kidneys to the dorsal aorta 

 and from a vein joining the cardinal vessel at the front end of the enlarged, rear part of the kidneys. 



The gas-gland has two lobes, the left being the larger. This is an elongated band of tissue with an 

 enlarged and rounded posterior part, which lies immediately in front of the rete mirabile and invests 

 the lateral walls of the sac. The right lobe is a triangular patch of tissue lying opposite the tip of the 

 left lobe. The length of this lobe is 1-3 mm. as compared with the 3-2 mm. span of the other one. 



Each lobe receives blood-vessels leaving the forward end of the rete. The artery and vein to the 

 right lobe run along the lateral walls of the sac. 



The resorbent capillary network, which lies just under the inner epithelium, covers most of the 

 swimbladder roof. The by-pass vessel from the retial artery runs forwards along the right side of 

 the rete and then describes an undulating course about the long axis of the sac. This artery gives off 

 arterioles on either side, which break up into capillaries. The circulation is completed by venules and 

 capillaries that come from vessels running along the upper edges of the gas-gland lobes. 



Astronesthes lucifer Gilbert (Text-fig. 12 A, b) 

 B.M. Reg. no. 1922.6.7. 14-23. Misaki, Japan. Standard length 73 mm. (16-5 X3>5 mm.). 



The swimbladder of this astronesthid is an elongated ellipsoid sac tapering to a point anteriorly. 

 Above the base of the pelvic fins and at the posterior end of the organ is a single, bulbous rete mirabile, 

 2-5 mm. in length and 1-3 mm. in width. This is fed with arterial blood by a vessel that extends 

 backwards and then turns upwards through the kidneys to join the dorsal aorta. The vein enters the 

 kidneys at the point where they begin to enlarge behind the swimbladder. 



The two lobes of the gas-gland, which extend over the floor and sides of the swimbladder, come 

 immediately in front of the rete mirabile. Along the upper and lower parts of each lobe are vessels, 

 which lead to the rete. 



Astronesthes gemmifer Goode & Bean (Text-fig. 12D) 

 Westmann Isles, Iceland. B.M. Reg. no. 1950.6.30. 2. Standard length 168 mm. (20x3 mm.). 



The swimbladder of this species was found over the posterior half of the stomach. It is an elongated 

 organ with very thick walls. At the posterior end of the bladder is a conical rete mirabile measuring 

 about 3-5 mm. in length and 1-5 mm. in greatest width. 



The gas-gland appears to be a solid rod-like structure, but actually consists of two closely con- 

 tiguous lobes which together fill most of the lumen of the sac. All the tissues appear to be very con- 

 tracted, or it may be that the organ regresses during adult life. 



