494 PISCES SUB-CLASS III.TELEOSTOML 



species. There are many representatives of the genus from tropical and tem- 

 perate seas, some of which ascend tidal rivers. All are highly predaceous. 

 The so-called glass-eels (Leptocephalus) are larval forms of the members of 

 the present family. Although occasionally brought by currents to the surface, 

 they live at great depths in the sea. Before turning into the adult form they 

 undergo a distinct metamorphosis. Nearly allied are the five representatives 

 of the genus Gymnomurcena, which inhabit the Pacific and Indian Oceans, and 

 have the median fins represented by mere rudiments near the extremity of 

 the tail. From both these genera the true eels (Anguilla) may be easily 

 distinguished by the retention of the pectoral fins, which are placed close to the 

 head, and have the narrow gill-openings just behind their roots. The two 

 jaws are approximately equal in length; the skin contains a number of rudi- 

 mental scales ; and the teeth are small and arranged in the form of bands. Eels 

 are so familiar to all that they need no further description. Before com- 

 panies were so careful in filtering their water as at present, eels would, not 

 unfrequently, enter the service-pipes, where they would remain until the pas- 

 sage became completely choked, owing to their increase in size. Eels occur 

 in the fresh waters of all parts of the world where the temperature is not per- 

 manently below the freezing point. Reams of paper have been spoilt in dis- 

 cussing their breeding-habits, which long remained a mystery. It is, how- 

 ever, now ascertained that eels breed only in the sea, and that the repro- 

 ductive process seems to be fatal to their existence ; such individuals as are 

 confined to fresh waters being sterile. In autumn such adults as are enabled 

 to find a passage make their way to the ocean, whence they never return ; 

 while in spring the elvers, or young eels, ascend the rivers, frequently in enor- 

 mous numbers. On such migrations scarcely any obstacles will stay their ad- 

 vance, and they have even been 

 known to circumvent a barrier by 

 leaving the water and making a 

 detour over moist rocks or marshy 

 ground. Thus St. John writes that 

 in a Scotch river when the elvers 

 " came to a fall that they could not 

 possibly ascend, they wriggled out 

 of the water, and gliding along the 

 rock, close to the edge where the 

 stone was constantly wet from the 

 Fig. 24. SERPENT-EEL. splashing and spray of the fall, they 



made their way up till they got above 



the difficulty, and then again slipping into the water, continued their course." 

 Writing of eel-migrations in the Thames, Jesse observes that this takes place 

 in May. " The young eels are about two inches in length, and they make 

 their approach in one regular and undeviating column of about five inches in 

 breadth, and as thick together as it is possible for them to be. As the pro- 

 cession generally lasts two or three days, and as they appear to move at the 

 rate of nearly two miles and a half an hour, some idea may be formed of their 

 enormous number.'' The largest eels occur in Oceania, where examples 

 measuring as much as ten feet in length have been recorded. From the true 

 eels the marine species included in the genus Conger differ by the total want 

 of scales, as well as by the larger mouth, the presence of an outer series of 

 cutting teeth in the jaws, and the more forward extension of the dorsal fin. 

 At least four species of conger are known, among which C. vulgaris is almost 



