— i89 — 



d. Other species of Leptocephali ' 



It will be convenient to say a few words liere concerning the other Leptocephali, in 

 all 5 forms taken by the ''Thor". They are all figured on Plate IX, where photographs 

 direct from nature are reproduced almost in natural size. Of the 5 species 3 belong to 

 the genus Leptocephalus, 2 the genus Tiiurtis, which is remarkable amongst other cha- 

 racters by having a long whip-like tail and by the absence of an anal fin. I shall not 

 enter upon any detailed description of their structural features here. 



Previous to the cruises of the "Thor" only one species of Leptocephalus was known 

 from the Atlantic off North and West Europe, namely L. Morrisii the larva of the 

 conger, which had now and then been found on the coasts of Great Britain as also a 

 single time at Norway (CoUett 1903). The investigations with the "Thor" hawe now 

 shown, that various species of Leptocephalus occur in the northern Atlantic 

 off West and North Europe, where like the Leptocephalus of the com- 

 mon eel they live pelagically in the middle and upper layers over great 

 depths. Our 5 Leptocephalus species have pracfically always been found together with 

 Lept. brevirostris, in greatest number off the south-west coast of Ireland. We have only 

 once taken a Leptocephalus (larva of the conger) in a haul where L. brevirostris did 

 not occur at the same time, namely, north-west of Ireland at St. 77 (55°04' N., 9°58' W., 

 depth 116 meters). For the rest, the Leptocephali other than brevirostris have been 

 taken by the "Thor" along the whole distance from west of the Faeroes to off Brittany. 



It is of interest to note the relative quantities of Lept. brevirostris and the other 

 Leptocephali. I shall here mention the various species separately ^ 



1. Leptocephaltts Congri vulgaris (L. Morrisii) (PI. IX, Fig. 8— 9) 

 Of this form we have taken in all 1 1 specimens, all in June 1905. In all the anus 

 lay far back as is shown by the photographs on Plate IX. The metamorphosis had thus 

 not yet begun. 



Place of capture (all in June 1905): St.8>, 300 ni. wire, 2 specimens. St. 77, 65 m. wire, i specimen. 

 St. 82, 300 m. wire, 3 specimens. St. 88, 300 m. wire, 3 specimens. St. 92, 300 m. wire, i specimen. St. 93, 

 200 m. wire, i specimen. 



larvae may possibly be driven far from the places where they are born and that we therefore cannot conclude 

 from the places of their discovery where the old eels spawn. In answer to this the following may be said: 



(i) it is not known whether there are in reality any strong currents in the deep water where the eel eggs 

 and the tiny fry occur. Only when the larvae mount up into the middle and surface layers can there perhaps 

 be any question of the direct influence of the currents; 



(2) the eel larvae were found in September over exactly the same depths as in June (but were then in a 

 different .stage of development). This does not seem to indicate any great drift; 



(3) even if we considered that the eel larvae were really carried a long distance, they could not in any 

 case be driven from the coastal waters of Europe out into deep water where we found them, i. e. to the west, as 

 the Atlantic Stream goes in the main in the opposite direction. If the larvae had really been carried a long 

 distance they must have been born in still greater depths than those where we found them. 



1 The two most important of recent works on Leptocephali in which a list of the literature is given 

 are: P. H. StröMMAN, "Leptocephalids in the University Zoological Museum at Upsala", Upsala 1896, with 

 5 plates, and C. H. Eigen'MANx and C. H. Kennkdy, The Leptocephalus of the American Eel and other 

 American Leptocephali (Bull, of the U. S. Fish Commission, vol. XXI for 1901, Washington, 1902, p. 81 — 92). 

 Further, L. Facciola has published a large number of papers in Italian (Sicilian) journals to which I have 

 not had access. 



2 For the position of the stations, see list of the catches of L. brevirostris. 



