SURVEY OF STRUCTURE 21 



surface between the ventral and lateral sections of the gas-gland. The entire capillary circulation, 

 which seems to be much like that of A. aculeatus, must form an effective inner surface for the diffusion 

 of gases into the blood. 



Argyropelecus sladeni Regan 



St. 285, 2 43' 30" S., oo° 56' 30" W., 16. viii. 27, N450H, i75-i25(-o) m. B.M. Reg. no. 1930.1.12. 401-6. 

 Standard length 20 mm. (175 x 1-5 mm.). 



The swimbladder of this species is almost spherical and lies above the stomach in the upper half 

 of the body cavity. 



The single rete mirabile receives an artery from the dorsal aorta and a vein that originates between 

 the kidneys. The retial complex formed from these two vessels is cylindrical and enters the floor of 

 the sac from behind to supply the gas-gland. This covers part of the floor and extends backwards 

 and upwards over the side and rear walls of the sac. Viewed from above through a hole cut in the roof 

 of the sac, vessels leaving the rete can be seen running forwards over the floor to the ventral part of 

 the gland. 



The two non-glandular areas on either side of these vessels are invested with a capillary net- 

 work, which has been described more fully under A. aculeatus. 



Argyropelecus hemigymnus Cocco 



Nusbaum-Hilarowicz (1920) found the swimbladder of this hatchet fish to be dilated anteriorly and 

 narrowed posteriorly. Two ligaments of connective tissue attached to the front part of the sac extend 

 upwards to a fastening on the roof of the body-cavity. The walls are constructed of an outer layer of 

 long fibres (mainly running around the sac), a middle and thick layer of loose connective tissue and 

 an inner epithelial layer which forms the gas-gland. This covers the floor and lateral walls of the 

 forward part of the swimbladder, there being a small, median, ventral lobe and two larger lateral 

 lobes. A single long rete mirabile enters the rear part of the swimbladder and runs forwards under the 

 floor to the gas-gland. 



Sternoptyx diaphana Hermann (Text-fig. 10 c, d) 



St. 281, oo° 46' 00" S., 5 49' 15" E., 12. viii. 27, TYF, 950-850^0) m. B.M. Reg. no. 1930.1.12. 416-25. Stan- 

 dard length 14 mm. (2-7 x 2-5 mm.). 



St. 269, 15 55' 00" S., io° 35' 00" E., 26. vii. 27, TYF, 700-6oo(-o) m. B.M. Reg. no. 1930.1.12. 413-15. Stan- 

 dard length 39 mm. (9-0 x 5-0 mm.). 



The swimbladder is a heart-shaped organ lying in the upper half of the body-cavity. The long axis 

 of the sac, which is thin-walled, is directed downwards and slightly backwards, so making an acute 

 angle with the vertical axis of the fish. 



There is a pair of suspensory ligaments running from the roof of the body-cavity to an attachment 

 on the posterior part of the roof of the swimbladder. The other suspensory structures, which are more 

 in the nature of mesenteries, are attached to the anterior middle region and the bottom of the sac. 

 Both taper to points of attachment on the peritoneum of the body-cavity, the former to a point 

 opposite the top of the stomach, and the latter to a point behind the basal part of the intestine. 



The single, club-shaped rete mirabile, which has a length of 2 mm. in the larger fish, enters the 

 roof of the swimbladder. It receives a branch from the posterior cardinal vein and an artery (running 

 between the kidneys) from the dorsal aorta. The gas-gland invests the roof and is composed of three 

 lobes, each receiving blood-vessels from the rete mirabile. 



The fine structure of the swimbladder of this species has been described by Nusbaum-Hilarowicz 

 (1920). Besides noting the bipolar structure of the rete mirabile, he saw that certain of the outgoing 



