224 SUB-CLASS (AND ORDER) TELEOSTEI. 



arrive at maturity at a less depth, but has to migrate to a greater depth 

 to fertilise the eggs. The eggs float, but at a considerable depth and only 

 exceptionally mount to the surface. The characteristics of typical Lepto- 

 cephali are the transparent ribbon-shaped body with colourless blood, 

 vent near the tip of the tail, small head, and large eyes. 



It has long been suspected that certain Leptocephali were the larvae 

 of the conger, but many held that they were abnormal overgrown larvae 

 incapable of further development, on the ground that they attained a 

 size larger than that of the youngest conger, and because of the great 

 variability of their form and dentition. The first naturalist who definitely 

 observed the metamorphosis of a Leptocephalus into a young conger was 

 Delage in 1886 (Comptes Bendus, 103, 1886, p. 698). In this metamor- 

 phosis the skin became pigmented, the blood coloured, the air-bladder 

 developed, and the body cylindrical and shorter. 



Grassi has shown that L. stenops (in part), L. morrisii and punctatus 

 belong to the life-cycle of Conger vulgaris ; that L. haeckeli, yarrelli, bibroni, 

 gegenbaurii, kdllikeri, stenops (in part) belong to Congromuraena mystax ; 

 L. taenia, inornatus, and diaphanus to Congromuraena balearica, etc. 



Fam. 21. Derichthyidae. Body eel-like, from the abysses of the 

 Atlantic ; Derichthys Gill. 



Fam. 22. Muraenidae, with the characters of the sub-order. (This 

 family is now usually divided into several.) 



Group 1. Eels in which the branchial openings in the pharynx are 

 wide slits. 



Nemichthys Rich., jaws produced into long slender bill, eyes large, with 

 Serrivomer, Spinivomer, Avocettina, Labichthys are deep-sea (500-2,500 

 fms.) forms. Anguilla Cuv., eels, small scales imbedded in the skin, 

 upper jaw not projecting beyond the lower ; gill-openings narrow, at the 

 base of the pectoral fins ; dorsal fin some distance from head ; they freely 

 ascend rivers, descending to the sea for purposes of reproduction ; f . w. 

 and coasts of temp. and trop. zones, not yet found in S. Amer., W. coast of 

 N. Amer. and W. Afr. A. anguilla L., the common Eur. and Brit, 

 species, they descend rivers in the autumn and spawn in the deep sea ; 

 the larva is known as Leptocephalus brevirostris ; the young eels are 

 called elvers, and ascend rivers in incredible numbers in spring (April 

 and May), overcoming all obstacles and even crossing land ; such migra- 

 tions are known as eel-fares (of which elver may be a corruption), they 

 bury themselves in mud and become torpid in winter, do not develop 

 their generative products in freshwater ; the adult eels are said not to re- 

 ascend rivers and to die soon after spawning. 



In eels migrating down the rivers to the sea the reproductive organs 

 are enlarged, and the skin has a silver colouration. The eyes also are 

 enlarged. All these peculiarities are observed in the sexually mature 

 forms taken from the deep water. Young elvers are not known of a less 

 size than 5 cm., while the larva, L. brevirostris attains a length of 8 cm. 



Simenchelys Gill, and Ilyophis Gilbert, are deep-sea eels ; Synapho- 

 branchus Johns., gill-openings united into a longitudinal slit, deep-sea 

 congers ; Conger Kaup., congers or marine eels, scaleless (Leptocephalus, 

 Oxyurus, Helmictis, are all said to have priority over Conger), C. conger 

 L., prefers deep waters with rocky bottom, attains to 8 ft., almost cosmo- 

 politan ; allied genera are Poeciloconger, Congromuraena, Uroconger, 

 Heteroconger ; Muraenesox McClell., scaleless, trop. seas ; Nettastoma 

 Kaf., scaleless, deep-sea, the leptocephalid form is Hyoprorus ; Sauren- 



