— 143 - 



where it was marked, southwards through the Baltic and then to the north in the Danish 

 waters where as mentioned it was taken on the east coast of Jutland. This distance must 

 be considered as at least llSo— 1200 kilometers'. 



Whilst we thus have direct proof that the breeding eels of the Baltic migrate quite 

 out of the Baltic in order to go with the Danish eels towards the north in the Danish 

 waters, we have no hope of being able by marking-experiments to follow the eels in their 

 further migration out towards their spawning grounds. Outside the Danish waters 

 there is no fishery after the silver eels in the sea and the fishing apparatus 

 used in the open sea (North Sea etc.), such as trawl and drift net, are not suited to the 

 capture of eels. In the countries lying round the North Sea and on the Atlantic Ocean 

 nothing is therefore known concerning the fate of the eel after it has left the fresh water 

 and shallow coastal waters. 



We thus come to a point where both the fishermen and the scientists are brought 

 to a stop and where we cannot expect any further information on the biology of the eel 

 by means of the practical fisheries as carried on at present. These are quite unable to 

 assist the scientists desirous of investigating further the breeding of the eel. We thus see 

 also, that all the investigators who have endeavoured to obtain material from the prac- 

 tical fishermen have failed to get any further forward in the matter than to find eels, 

 which were still far from quite mature. 



Thus with regard to the male sexual organs no one had yet succeeded in finding 

 spermatozoa 2, nor in the female eggs which were larger than '/s '"nrn- in diameter, much 

 smaller as a rule and never clear as the eggs of other species are known to become 

 before spawning. No one had yet described the eggs of the eel in a condition 

 near to spawning or even approximately mature. None of the cases3 of ripe 

 female eels mentioned in literature as coming from shallow water have stood the test of 

 criticism. The result is therefore, that so many eels have in past years been examined 

 from fishermen's apparatus in the coastal waters of Europe without any being found at 



1 According to the calculation of F. Trybom: Almärkningar i Östersjon 1905 (Svenska hydrogralisk- 

 biologiska Kommissionens Skrifter III 1906). In this paper it is explained that this eel was marked on Aug. 15th, 

 1905 and retaken on Nov. i6th and had thus traversed a distance of ca, 1200 kilometers in 93 days. According 

 to Trybom an eel marked at Bergkvara in Kalmar Län on Sept. loth, 1905 vi^as retaken at Helsingborg 

 (northernmost part of the Sound) on Oct. 9th, 1905 and had thus traversed 367 kilometers in 29 days. Try'BOm's 

 latest results from 1905 confirm the calculation that the eels often migrate at a speed of ca. 15 kilometers per 

 day and further that the Baltic eels for the most part at least pass through the Sound. 



2 That the "lobed organ" of the eel observed by Syrski is really the testes is proved by several things, 

 thus by comparison with the fully ripe conger and spermatic tubuli have further been found in them. The 

 lobes had not been found to exceed ca. 3 mm. in breadth. 



3 cf. C .G. JoH. Petersen (Rep. Dan, Biol. Stat. V, fcr 1894, 1896, where older notices, e. g. Rathke's, 

 are mentioned). More recently a paper by EuGENE G. BLACKFORD has been published: "Note on the spawn- 

 ing season of the eel" (Science, N. S., vol. IX, p. 230, 1899), which mentions the discovery of an eel (length 

 42 cm,, weight 135 gm.) in 2 — 3 fathoms at Atlantic Highlands (U. S.) on May 8th, 1898. According to the 

 author the eggs of this eel had a diameter of 4 [4] mm in contrast to the usual o'3 [-03] mm. and an invest- 

 igation "shows that the germination vesicle is clearly defined, and that the egg is all but mature". "The 

 color of the specimen was relatively bright, but not unusually so, nor was the eye notably larger than in 

 similar specimens from the same locality". The author concludes that this find shows, that the eel may 

 exceptionally at any rate become ripe in shallow depths and further that the season of ovulation is many 

 months later in the American eel than is the case in the Mediterranean. The author's description however is 

 too imperfect to be convincing. 



