EEPRODUCTION AND DEVELOPMENT OF THE OONGEE. 39 



laterally compressed fishes^ one of which, Cepola ruhescens, is 

 British. 



But the identification of Leptocephalus with Cepola was obviously- 

 erroneous on anatomical grounds, and was completely rejected by 

 other zoologists. An American ichthyologist, Gill, after examining 

 the subject, came to the conclusion (Proc. Acad. Nat. Sc. Philadel- 

 phia, 1864) that the typical Leptocephali were the young of congers, 

 and the one considered here, Leptocephalus Morrisii, the young of 

 Conger vulgaris ; he referred Hyoprorus, another genus of the Lepto- 

 cephalidee, to another genus of the Muraenidae, namely, Nettastoma, 

 which lives in the Mediterranean. 



Gill did not give the anatomical comparisons on which his conclu- 

 sions were based. In his British Museum Catalogue of Fishes, 

 vol. viii, 1870, Dr. Giinther confirms Gill's conclusion so far as con- 

 cerns the derivation of Leptocephalus Morrisii from the conger, but 

 doubts whether the conger is developed from the Leptocephalus. Dr. 

 Giinther mentions as evidence for the connection between the two 

 forms, the similarity in the form of the head and its parts, the coin- 

 cidence in the number of vertebrse (156) and the geographical 

 distribution. But he says the question arises whether the Lepto- 

 cephalus is a normal stage in the development of the conger, or 

 whether it is an individual arrested in its development at a very 

 early period, yet continuing to grow to a certain size without a 

 corresponding development of its internal organs, and destined to 

 perish without attaining the characters of the perfect animal. 



The reasons Dr. Giinther gives for the latter view are three : — 



(1) That he has seen a specimen of a conger A\ inches long, 

 i. e. smaller than numerous specimens of Leptocephalus Morrisii. 



(2) Specimens showing apparently a more developed condition, an 

 approach towards the conger, in the more cylindrical body and more 

 elongated snout, nevertheless have still an undeveloped vertebral 

 column ; if Leptocephali are abnormally undeveloped forms, some 

 individuals may be more developed than others in certain points. 



(3) The variations in the form of the body, dentition, &c., are so 

 great that it is impossible to separate them into specific forms, and 

 this great variability favours the supposition that they are indi- 

 viduals abnormally arrested in their development. 



This hypothesis concerning Leptocephali is still more confidently 

 maintained in Giinther's Introduction to the Study of Fishes, pub- 

 lished in 1880. The same hypothesis has been put forward in two 

 other cases, namely, in that of the large Phyllosoma forms, known 

 to be derived from the Loricate Crustaceans, such as Palinurus, and 

 in that of large TornariXy known to be the larvae of Balanoglossus. 

 In the case of the Tornaria it was found on investigation that the 



