336 A HISTORY OF FISHES 



of changes, but the body is covered with small, rough warts 

 arranged in regular lengthwise rows, these being still apparent 

 after the individual has assumed all the other features of the 

 mature fish. 



The Gar-fishes [Belonidae) also possess long beak-like jaws, but 

 a study of the development of these fishes reveals the fact that 

 it is the lower jaw which is first prolonged and the upper 

 afterwards grows out to equal it. Thus, during its development 

 the Gar-fish passes through a temporary stage in which, as 

 far as the jaws are concerned, it is exactly like the adult 

 Half-beak {Hemirhamphus) . It might be assumed that the Half- 

 beaks are ancestral to the Gar-fishes, but it is more probable 

 that the unequal jaws of the larval Gar-fish are associated with 

 some specialised feeding habit, and that this condition was later 

 retained by some of the primitive Half-beaks in the adult stage. 



In the Ten-pounders (Elops), Lady-fishes {Albula), and in all 

 the Eels {Apodes), the larvae are of a peculiar, transparent, 

 leaf-like form, quite unlike the mature fishes, and the period 

 of larval life is greatly prolonged. Further, these larvae may 

 grow to a relatively large size, in certain species attaining to a 

 length of a foot or more. This type of larva is known as a 

 Leptocephalus (leaf head), and the first specimen of its kind was 

 discovered by a naturalist called Scopoli in 1777, but he 

 regarded it as representing a distinct group of fishes. The 

 first British Leptocephalus was discovered in 1 763 by one William 

 Morris near Holyhead, but this was not described until 1788, 

 when Gmelin named it after the finder, Leptocephalus morrisii. 

 It was not until 1861 that Carus first recognised that these 

 creatures were larval forms, but he was mistaken in regarding 

 them as young Ribbon-fishes. In 1864 Gill expressed the view 

 that they were larval Eels, and established the fact that- Lepto- 

 cephalus morrisii was the young stage of the Conger Eel (Conger). 

 Dr. Gunther accepted this explanation, but held that they were 

 abnormally developed forms, "arrested in their development 

 at a very early period of their life . . . and perishing without 

 having attained the character of the perfect animal." This 

 view was soon disposed of, when the French scientist, Yves 

 Delage, succeeded in keeping a specimen of the Conger larva 

 alive in an aquarium for seven months, and watched the whole 

 process of transformation into the adult state. The next step 

 in the solution of what came to be known as the "Eel question," 

 occurred when an Italian naturalist, Raffaele, described the 

 eggs of five species of Eels, which he succeeded in hatching and 



