THE EEL FAMILY. 455 



history of the murisenoids (leaving out the common eel) as 

 follows : 



' Females can only mature in very profound depths of the 

 sea, that is to say, at least a depth of 500 metres. This fact I 

 established by finding well-known deep-sea fishes together with 

 Leptocephali, ripe Murcence, and quite ripe eels. The females 

 of those species which do not live at this depth must therefore 

 migrate to it. The male, however, can mature at a smaller 

 depth and therefore they migrate into the greater depth when 

 they are already mature. Fertilization takes place at great 

 depths : the eggs float in the water ; nevertheless they remain 

 at a great depth in the sea, and only exceptionally, for unknown 

 reasons, some of them mount to the surface'.' 



The earliest free form definitely connected with the conger 

 is one of a small group of fishes known as the Leptocephali. 

 This group has a history in some respects closely similar to 

 that of the mackerel-midges : like them they were first 

 described as adult forms or abnormalities, and later, with 

 increase of knowledge, they have been shown to be the young 

 stages of well-known species. The first recorded specimen 

 of British leptocepbalid was caught by a Mr William Morris, 

 in the neighbourhood of Holyhead. This fish was given the 

 name of 'the Morris' by the celebrated naturalist, Pennant, 

 and Leptocephalus morrisii by the Dutch observer, Gronow, by 

 whom it was described. The description has proved to be 

 inaccurate and we need not detail it here. These events took 

 place in the middle of the eighteenth century and in the next 

 fifty years several isolated specimens appear to have been 

 caught from time to time, apparently on the bottom. 



Early in the 19th century two specimens caught at the 

 surface fell into the skilful hands of the late Colonel Montagu, 

 whose name is also connected with the history of the mackerel- 

 midges. He gave a correct description of them. Couch, at a 

 later date, obtained and described four specimens, naming them 

 Ophidium pellucidum, but afterwards establishing their identity 

 with Leptocephalus morrisii. Prof. Carus in a short article 

 upon the group Leptocephalus pointed out reasons for believing 



' Op. cit. 



