— 154 — 



What we know concerning the occurrence of the eel larvae in the Atlantic is thus 

 exceedingly little and quite insufficient to determine, on the one hand what the oceanic 

 conditions are which influence the occurrence of the larvae (or spawning of the eel) and 

 on the other hand whether it is right, as Grassi and Calandruccio suppose from their 

 investigations in the Messina Straits, that the larvae {Leptoccph. brevirostris) normally 

 live at or in the bottom, or whether their normal habitat on the contrary is in the upper 

 water-layers. 



There is on the whole great uncertainty as to the question, whether the various 

 Leptocephalus species are true pelagic forms or not. The naturalist who has, so far as 

 known to me, endeavoured the most critically to bring light into the various conflicting 

 reports on the occurrence of the Leptocephali and their mode of life is Cunningham ^ 

 In his account of Grassi and Calandruccio's work he thus writes: "That the larvae of 

 the conger and common eel are not constantly pelagic at night seems proved by the fact 

 that they have never been taken in abundance in nocturnal tow-netting expeditions. I 

 conclude therefore, that these Leptocephali and all those known from the Mediterranean, 

 are not truly pelagic, but live on or in the sea bottom and that the reason, they are 

 found in the open water or at the surface at Messina is that there the strong tidal cur- 

 rents and eddies stir up the bottom and carry their light bodies about as scraps of paper 

 are lifted and borne along by the wind. Reference to my previous paper, and the records 

 which are there cited, will show that in two cases L. Mornsii has been taken in a hand- 

 net near the surface of the water, but in other cases it was taken from the bottom, for 

 instance, in the process of fishing prawns. There can be little doubt that the larvae of 

 the conger and of the eel exist around our coasts in great abundance under stones or 

 buried in sand or gravel, and that we do not catch them because we do not know the 

 right way to go about it." 



On the other hand, however, Cunningham refers with perfect right to the fact that 

 according to all reports on collections in the open waters of the tropics Leptocephali are 

 found in quantities on the surface and are taken there in pelagic nets. He then 

 express the following conclusions (1. c. p. 286) : "It seems evident that in tropical regions 

 of the ocean truly pelagic Leptocephali are of constant occurrence and fairly abundant. 

 It will probably be found that these are the larvae of species of Muraenidae other than 

 those whose larvae have been traced by the Sicilian naturalists". Even this explanation, 

 however, is not completely borne out, as Cunningham himself remarks, for certain species 

 of Leptocephali such as Leptocephalus taenia and others are found on the surface in 

 the tropical seas besides in the Mediterranean. It would therefore be quite unreasonable 

 to suppose that they should at the one place have a quite different mode of life from that 

 at the other. 



From the following account of the investigations of the "Thor" in the Atlantic Ocean, 

 we shall see that Cunningham was right in supposing that the larvae of the common eel 

 occur in quantities off the British coasts, and also, that several questions concerning the 

 normal mode of life of the Leptocephali receive their final solutions. 



I J. T. Cunningham, The Larva of the Eel (Journal of the Marine Biological Association of the United 

 Kingdom, 1893—95, vol. Ill (No. 5) p. 285). 



