194 MARKETABLE BRITISH MARINE FISHES 



Evidently their powers of swimming are not great. There are 

 differences of shape and structure among them, and a number of 

 species based upon these have been described. Only one kind 

 has been taken on English shores, and this kind, formerly called 

 the Morris, occurs also at Messina. In England only a feu- 

 specimens have been taken since it was first discovered in 1763. 

 It is usually 5 or 6 inches long and i inch broad. 



Various theories were formerly proposed concerning the nature 

 of the Leptocephali. In 1861 it was suggested that they were 

 the larva.' of certain fishes which had an elongated narrow band- 

 like form in the adult condition, namely, fishes of the same 

 family 'as the red band-fish of British waters (Cepola). But the 

 anatomical peculiarities, such as the position of the vent and 

 absence of pelvic fins in the Leptocephali y did not agree with 

 this supposition, and in 1864 an American naturalist announced 

 his opinion that they were the young of the eel family, and in 

 particular the English form Morris, the young of the conger. Dr. 

 Gianther in 1870 expressed his agreement with this view with 

 regard to the derivation of the Morris, from the conger, but was un- 

 able to accept the idea that the Leptocephali were the natural 

 ordinary condition of the young of fishes of the eel family, 

 because they are so large, and he had seen young conger smaller 

 than the known specimens of the Morris. He suggested there- 

 fore that the Leptocephali were monstrosities, were larvae which 

 having got into unnatural conditions had gone on growing in 

 the larval state without going through their proper transforma- 

 tion. 



In 1886 however, at Roscoff in France, a specimen of the 

 Morris was kept alive in the aquarium and actually observed to 

 change into the conger, and in 1891 and 1892 Grassi and 

 Calandruccio, two Sicilian naturalists, made very careful and 

 successful experiments on the Leptocephali taken at Catania, 

 and actually observed the transformation of different kinds of 

 the larvae into different kinds of eel-like fishes found in the 

 Mediterranean, including the conger. The difficulty pointed out 

 by Dr. Giinther is explained by the fact that the Leptocephali 

 take no food during their transformation, and become very much 

 reduced in size. Such a reduction in si/.c during transformation 

 is known in other animals. 



The habits of the Leptocephali arc not fully explained. In 



