30 DISCOVERY REPORTS 



Suborder CLUPEOIDEA 



Family Alepocephalidae 



Alcock (1899) stated that the Alepocephalidae have no swimbladder. Beebe (1933) examined the 

 internal organs of Bathytroctes rostratus and Xenodermichthys copei, but made no mention of a swim- 

 bladder. I was unable to find any trace of this organ in an adult of the latter species, nor in Searsia 

 koefoedi. 



Order INIOMI 

 Suborder MYCTOPHOIDEA 

 Family Myctophidae 

 Myctophum punctatum Rafinesque (Text-fig. 15A-C) 

 St. 3233, 46 02' N., 09 19' W., NH, o m. Standard lengths of fishes 74-5, 71-0, 69-0 and 59-0 mm. 



In this lantern fish a capacious swimbladder is found above the stomach. The anterior end is 

 opposite the margins of the gill-covers, while the posterior extremity lies under the origin of the 

 dorsal fin. The sac is thin-walled and ellipsoidal in form, the major and minor axis measuring n-o 

 and 4-5 mm. in the 69-o-mm. fish. 



Three retia mirabilia are found on the underside of the forward, rounded end of the sac. The retial 

 blood supply comes from an artery running backwards and downwards from the dorsal aorta and 

 returns through a vein that joins the hepatic portal system. 



In the 74-5-mm. fish, each of the three retia mirabilia (which have a length of about 2 mm.) runs 

 to a corresponding lobe of the gas-gland. The middle lobe is shaped rather like a rose petal and lies 

 over the floor, while the left and right lobes, which are fan-like, extend over the lateral walls. As in 

 all lantern fishes, the surface of the gland has a convoluted appearance, due to the meanderings of the 

 capillary loops with their associated investments of gland cells. This kind of rete in which the arterial 

 and venous capillaries run straight to the gas-gland without forming larger vessels is termed unipolar. 



Above the retia mirabilia is a resorbent ' oval ' which is partly expanded. It measured 2-5 mm. along 

 the longitudinal axis and 2-2 mm. in width. The oval bears a fine-meshed network of capillaries fed 

 by two branches of the retial artery. The venous return is through a large vessel running upwards 

 and forwards to a point between the kidneys, presumably to the posterior cardinal vein. 



In the 69-mm. fish the oval is partly expanded and the opening into the swimbladder has a diameter 

 of 2-5 mm. The capillary-bearing tissue is an egg-shaped blister measuring 3-5 along the longitudinal 

 axis and 3-0 mm. in greatest width. The oval of the 59-mm. fish is shut, the inner surfaces of the 

 walls being thrown into folds. The fine structure of the oval in the closed phase will be dealt with 

 in more detail in a later section (p. 80). 



Diaphus rafinesquei (Cocco) (Text-fig. 1 5 D, e) 

 St. 3484, 39 55' N., 20 01' W., 1. x. 56, IKMT, 75o(-o) m. Standard length 70 mm. 



A detailed description of the swimbladder of this myctophid has been given by Rauther (1922). 

 According to his reconstruction of transverse sections (shown in his fig. 13), the swimbladder of his 

 fish measured about 7 mm. in total length. The middle depth was rather less than 1 mm. In the 

 Discovery fish the length of the sac is about 20 mm. and the middle depth about 7 mm. Rauther 

 showed the walls of the swimbladder to be relatively thick, but the sac was clearly not in an expanded 

 condition. There was an outer fibrous layer which did not cover the roof, and then came two layers 

 of loose and closely packed connective tissue fibres. 



