— 239 — 



for them (or could not seek for them) at the right places. Further it has already been 

 mentioned by Grassi and Calandkuccio, that the male of the Muraenoids in contrast to 

 the female could mature in shallow water, and as regards the conger this has been directly 

 described by Hermes and Cunningham, who kept the animals in an aquarium, but did 

 not succeed in getting the female fully ripe. 



9. Relation betw^een the European and American eel (AnguiUa vulgaris, Flem. 



and chrysypa, Rafinesque) 



a. Adult fishes 



It was of considerable interest for the present questions to obtain some precise 

 information regarding the relation between the European and American freshwater eels. 

 If the conclusions our investigations of the Leptocephali in the Atlantic indicated, namely, 

 that the eel spawned near the Atlantic slope, were correct, then the central part of the 

 Atlantic must constitute a barrier between the stock of eels in Europe on the one side 

 and America on the other, and we should therefore expect to find definite anatomical or 

 morphological differences in eels from the two sides of the Atlantic. 



From what was already contained in the literature on this question, there did not 

 seem much hope of getting very far in seeking for differences in the position of the fins 

 or anus; but the measurements available were nevertheless so incomplete that a more 

 exact investigation was very necessary, especially as no attention had been paid to the 

 possible differences between the sexes nor to the changes in the position of the fins 

 and anus with increasing size, such as are known to occur frequently in fishes. 



The number of vertebrae seemed to offer better prospects according to the available 

 information (the ichthyological handbooks of Kr0yer, Günther, Lilljeborg, Smitt etc. and 

 the more recent investigations of Grassi and Calandruccio (1. c. p. 10) and Eigenmann 

 and Kennedy (1. c. p. 84.)'. According to these investigations the number of vertebrae 

 varies between 112 and 117 in the European eel and between 105 and no in the 

 American eel 2, but the numbers of specimens examined was far too small to be able to 

 represent the extent of the variation in the two forms, and further the males and females 

 had not been distinguished in these investigations. 



As I had counted the vertebrae of a considerable number of European eels for other 

 purposes, it seemed to me of great interest to do the same also for the American eel, 

 and in order to make the comparison I procured ca. lOO specimens of the Canadian eel 

 through the Danish fisheries agent in London, Captain A. S0lling 3. Only the females 



1 The following numbers are given: (A) the European eel: 112 — 115 (Kr0YER), 113— 117 (Günther^, 

 113 (Lilljeborg), 112 — 117 (Grassi and Calandruccio), 114— 116 (Day), 112— 115 (Smitt); (B) t he- 

 American eel: 105 — no, in 8 specimens: 106, 107, 107, 109, no, 107, 105, 108 (EigenmaNN and 

 Kennedy). 



2 CO. JOH. Petersen (I.e. 1905, p. 3) found the following numbers from his investigation of elvers: 

 American eel: 103, 104, 106, io6, 109, 109, 113. 



European eel: 116, 117, 119. 



3 The investigation was carried out in the following manner. The eels were skinned and gutted, then 

 boiled and skeletonized with great care so as to avoid breaking the vertebral column. The flesh was quite 

 removed with a brush and the skeleton dried. To make the counting easier every loth vertebra was marked 







