TRANSACTIONS OF SECTION D. 409 



3. Five Year*'' Danish Investigations on the Biology of the Eel. 

 By Dr. J. Schmidt. 



About twenty years ago our knowledge of the natural history of the eels was 

 greatly advanced by the investigations of the Italian zoologist Grassi and his 

 pupil Calandruccio. Before that time nothing or almost nothing, was known, 

 and then all at once an answer was given to several fundamental questions : for 

 example, that the larval stages of the eels are the long-known Leptocephali ; by 

 a process of metamorphosis these become young eels. Further, it was shown 

 that Leptocephalua brevirostris was the larva of the freshwater eel and Lepto- 

 cephctlus morrisii the larva of the conger. Both of these species are very 

 common in our northern seas and in the Mediterranean, where the Italians car- 

 ried out their investigations. As is well known, the Italian observers obtained 

 their material from the Straits of Messina, and in two different ways : on the one 

 hand, from the stomachs of the Sunfish, which, as it feeds on Leptocephali, is 

 an excellent fishing apparatus for obtaining these animals. Further, the cur- 

 rents in the Straits of Messina, which have been known to be peculiar from the 

 most ancient times, were also of special use to them, as many marine animals, 

 even deep-water forms, are washed up on the shore at Faro, in the northern part 

 of the Straits, where they can be collected on the beach. 



A remarkable thing was that the Leptocephali were only known in quanti- 

 ties from the Straits of Messina, not from other parts of the Mediterranean. 

 And Grassi and Calandruccio thought that this was due in the main to the re- 

 markable whirlpools of the straits of Messina, which bring up the larvae from 

 (he deep water or bottom of the sea, to which they were supposed to belong. 



The discoveries of Grassi and Calandruccio naturally created quite a sensa- 

 tion everywhere. The puzzle, the reproduction of the eels, over which so many 

 had speculated for centuries, now seemed to have received its solution ; and 

 yet there was some considerable doubt about the matter, especially in Northern 

 Europe, where the two species of eels mentioned are very common and im- 

 portant. So far as the transformation of the Leptocephali to young eels is con- 

 cerned, this doubt has not been justified; in this respect our investigations in 

 the Mediterranean have fully confirmed the great discoveries of the Italian 

 observers. But, on the other hand, it has proved that the observations made 

 in the Straits of Messina could not be considered as holding good for the con- 

 ditions in North and West Europe, and that the solution given of the repro- 

 duction of the conger and freshwater eel was by no means the final one. 



In the years following the appearance of the work of Grassi and his pupil, 

 various experts on the biology of fishes, both in this country and on the Conti- 

 nent, endeavoured to explain why it was that the larvae of the conger and eel 

 were never, or practically never, found in the waters of Northern Europe. The 

 one who has dealt with this subject in most detail is, so far as I know, Cun- 

 ningham, who in a discussion of Grassi's work in 1895 made the following 

 statement : ' There can be little doubt that the larvae of the conger and of the 

 eel exist around our coasts in great abundance under stones and buried in sand 

 or gravel, and that we do not catch them because we do not know the right 

 way to go about it.' A similar explanation was given by several authorities 

 on the Continent — for example, in my own country — and there was agreement 

 so far in believing that the larvaa of the conger and eel would in time be found 

 in quantities in the waters where the old fish live. But of course these suppo- 

 sitions had nothing to go upon. The matter was then allowed to rest for some 

 years, until the international investigations with seagoing steamers and highly 

 developed methods of investigation brought us a step further. 



In May 1904, when the Danish research-steamer ' Thor ' was on its way from 

 the Faeroes to Iceland, we found a larva of the common eel to the west of 

 the Faeroes over a depth of 1,300 metres. In the same year this quite chance 

 discovery was followed by another, by Mr. Farran, to the west of Ireland, on 

 board the Irish* steamer ' Helga.' These larvae had only been known previously 

 from the Straits of Messina, and their discovery naturally led to a more sys- 

 tematic investigation, which has as far as possible been continued in each of the 

 following years. A very great deal still remains to be done before the biology 



