18 



III. The Eel compared with the Viviparous Blenny 



(Zoarces viviparus). 



A large number of samples of the European eel have now been examined 

 according to the variational-statistic method. The samples in question were talcen 

 from the most widely differing localities within tlie area of Anguilla vulgaris ; 

 thej' showed, however, the same result throughout, whatever the character selected 

 as the basis of investigation; whether number of vertebrae, number of branchiost- 

 egal rays, of pectoral, or anal rays. In no single instance, whether in the north, 

 south, east or west of the great area of the species, was a sample found to differ 

 in respect of the characters concerned from the samples taken elsewhere'. In other 

 words, it was found impossible to demonstrate the existence of any 

 racial difference. 



There seemed, then, no reason to proceed with the investigation of further 

 samples of A. vulgaris. On the other hand, it did appear desirable to institute, for 

 purposes of comparison, a similar statistic investigation of another species of fish 

 which, while resembling the eel as regards the figures for the characters in question, 

 yet difl'ered essentially in biological respects, there being reason to hope that such 

 comparison might bring to light features conducive to a further understanding of 

 the natural history of the eel. 



Such a species I found in the common viviparous blenny (Zoarces uiviparus). 

 This fish is, as regards the number of vertebrae and of pectoral rays, exactly 

 similar to the eel, differing, however, very considerably in biological respects, it 

 being, of course, viviparous, and having, in contrast to almost all our other species 

 of fish, no pelagic stage. It must therefore be presumed to be highly localised, 

 and tending to form local races. And as a matter of fact, it was soon found that 

 Zoarces was happily chosen for the purpose of such comparison, varying in a 

 surprising degree from place to place. 



In the following pages, some examples will be given from the very extensive 

 material of Zoarces which we have examined during the course of the past year. 

 A complete description of these investigations would be out of place here; such 

 will, howevei-, be given later on, when the work has been brought to a conclusion. 



The characters investigated in the case of Zoarces were as follows : 1) No. of 

 vertebrae, 2) No. of anal and dorsal rays, 3) No. of caudal rays, 4) No. of pectoral 

 rays, 5) No. of hard rays in dorsal fin, 6) No. of pigment spots in dorsal fin (from 

 the front to the concave portion). 



No variation being found in the number of branchiostegal rays, and the number 

 of caudal rays differing also but slightlj', these characters were not included. The 



' In my previous worlî, »On the classification of tlie fresh-water eels, (^Angiiilla.)<i (Meddel. fra 

 Kom. for Havundersogelser, Serie Fiskeri, Bind IV, No. 7, 1914), I referred, on p. 17 — 18, to some 

 investigations of B, Grassi, who was of opinion that différences between elvers of difierent origin 

 could be demonstrated by means of a longitudinal fissure generally found in the last hypural of the 

 elver. 1 have there full)' shown, h\' investigation, inter alia, of material from the same localities as 

 Grassi's, that no difference can be proved to exist In respect of the character In question. 



