— 149 - 



by Günther. This new method of investigation was shown in l886 by Y. Delage ' of 

 France, who kept a Lcptocephalus taken on F"ebruary 7th living in the Aquarium of the 

 Koscoff Laboratory in Normandy until September 5th. To begin with the fish was 

 ribbon-like and quite transparent, its blood being colourless. In May it already showed 

 some changes in its appearance, and the body-form gradually became cylindrical, the head 

 larger, the body more opaque and darker coloured. In July the originally flat, ribbon- 

 like Lcptocephalus had become a little Conger of 9-3 cm. in length which lived till Sep- 

 ember 5th. The experiment of Delage seemed thus to disprove Günther's theory, as his 

 Leptocephalus really developed into a young Conger, and this investigation 

 was the first step in the direction of experiment, which was later adopted with so great 

 results by the Italian Zoologists B. Grassi and S. Calandruccio. 



The investigations of these naturalists in the Mediterranean in the nineties of last 

 century increased our knowledge of the developmental history of the eels to such an 

 extent that a whole series of Leptocephalus-" species" could be referred to well-known 

 ■species of .eels ^. At the end of 1893 they published the epoch-making discovery that the 

 Leptocephalus brevirostris described by Kaup in 1856 (Kaup, Cat. Apod. Fish. Brit. Mus. 

 1856, p. 150, pi. XVIII, fig. 15) was the larval form of the common eel {Artgtälla vul- 

 garis). In their most detailed report (Riproduzione e metamorfosi delle Anguille; Giornale 

 Italiano di Pesca ed Acquicoltura, Nr. 7 — 8, 18973), they deal with the question in a 

 masterly manner and give a convincing proof of the correctness of. the results of their 

 researches. 



That Leptocephalus brevirostris is really the larval form of the common eel was 

 proved: (l)by an exact anatomical comparison between the Leptocephalus and the 

 common eel, in which amongst other things they found the same number of vertebrae; 

 (2) by finding various transitional stages in the Messina Straits between Ze^/'cce^/zrt/ai- 

 brevirostris and the youngest stage hitherto known of the eel, viz. the socalled elvers 

 which in the winter and spring come up from the sea into fresh water; and finally 



1 Y. Delage, Sur les relations de parenté du Congre et du Leptocéphale (Comptes Rendus, tome CHI, p. 690, 

 Paris, 1886). A paper was published in 1880 by Ch. Robin: "Note sur quelques caractères et sur le coeur 

 caudal des Anguilles, des Congres et des Leptocéphales" (Journal de 1' Anatomie et de la Physiologie, 6nie 

 année, 1880, p. 593 — 628), in which he inier alia compares the skeletal structure of the Conger young and 

 Leptocephaltis Mornsii and arrives at the conclusion that there is no agreement. (On the other hand he 

 naturally finds some agreement in this regard between the old eels and the young, transparent elvers: 

 „civelles".) 



2 According to the Italian authors the following are connected: 

 a. Leptocephalus stenops (Bellotti) in part, also L. Morrisii and 



L. ptmctattis to Conger vulgaris 



b. L. haecketii, yarrelli, bibroni, gegetibauri. köllikeri, stenops (in part) to. . Congrotmeraena inystax 



c. L. taenia^ iiioriialus, diaphamis Congromtiraena balearica 



d. L. kefersteini Ophichthys spec, divers. 



e. L. longirostris & Hyoprorus messinensis . . ' Neiiastoma melamirum 



f. L. oxyrhynchus etc Saurenchelys cancrivora 



g. L. sp. nov Muraena helena 



(Grassi, The Reproduction and Metamorphosis of the Common Eel {Anguilla -vulgaris), Proceedings of 

 the Royal Society, vol. LX, No. 363, p. 261, 1896), 



3 When nothing else is said, citations of Grassi and Calandruccio are always of this Italian work pub- 

 lished in 1897. 



