of the Fishery Board for Scotland. 



205 



The uncertainty of difference of colour as a sexual distinction lias 

 been shown by Cattie.* He found it impossible to discover distinctive 

 difference of coloration. All the males and females investigated by him 

 were of a white colour ventrally, green above, with a metallic lustre on 

 the sides. His experiments, on the same lines as those of Jacoby, 

 consisted of a comparison between male and female eels of equal size, as 

 regards width of snout between the nasal tubes, length of mouth from 

 middle of eye to tip of snout, diameter of eye, length of head to the gill 

 opening measured along the lower jaw, and height of dorsal fin. He found, 

 as Jacoby did, that the females have the dorsal fin higher and the snout 

 broader than males of the same length. The large-eyed character of eels 

 with lobulated organs appeared to him to be too uncertain a feature, so 

 much so, that according to his observations the same feature might be 

 assumed as characteristic of the females. * The snout of the female is not 

 4 only much broader, with more prominent eyes, but is also more depressed, 

 4 a characteristic to which I would call special attention, and one which I 

 ' do not find in the male. In contrast, the snout of the male eel is more 

 4 convex. By paying attention to the two most important characters, viz. 

 1 the relative proportions of the dorsal fin and snout, by their help picking 

 ' out those specimens which appeared to be males, I actually found 80-90 

 ' per cent, of those individuals so selected to be males with the Syrskian 

 4 organ.' 



Sennebogen f observed that when eels are left dry, the female specimens 

 give off far greater quantities of slime than the males, and that if the 

 severed skin is examined through a microscope, the scales of the females 

 are far smaller than those of the males. 



Petersen found that very distinct anatomical differences existed between 

 the yellow and silver varieties of eels. 4 J The sides of the yellow eel are 

 1 of a canary yellow colour, the back dark gray or brownish black. The 

 4 belly is sometimes yellow, oftener white, the colours on the whole varying. 

 ' Sometimes they have a slight metallic sheen, but as a rule this is absent. 

 ' In fresh water the yellow colour is not so often met with as in salt. If 

 4 the yellow eel is lean, the head appears abnormally large, and the eel has 

 1 a strange and repugnant appearance. Both males and females are found 

 4 among yellow eels. 



4 The silver eels are distinguished by a very strikiug metallic sheen on 

 4 the sides and belly. A bronze appearance is often seen in the neighbour- 

 4 hood of the lateral line in females as well as in males. The belly is usually 

 4 pure silvery white. The eyes of the silver eel are much larger than those 

 4 of the yellow eels of the same length, and rise up sideways so far that the 

 4 lips, which are very narrow, are for the most part not to be seen outside 

 4 the eyes if the head is looked at from above. The silver eel, according 

 4 to the fishermen, are always somewhat sharp-headed, are fat and in much 

 4 favour ; the thick-headed specimens, which are only found among yellow 

 4 eels, are in poor condition. The sexual organs of the silver eel are more 

 4 developed, and heavier than those of the yellow eels of the same size.' 



He found yellow eels of all sizes from 6 cm. upwards, but he discovered 

 no silver eels smaller than about 29-33 cm. in males, and 42-44 cm. in 

 females. He is led to the belief that the silver eel is the yellow eel in its 

 4 marriage dress' (Parungskleid). This explains why there are no silver 

 females whose total length is less than 42-44 cm., and no silver male* 



* Cattie, 4 On the Genitalia of Male Eels and their Sexual Characters.' Trans, in 

 Proc. U.S. Nat. Museum, vol. iii., 1880. 



t From 4 De strijd over de mannetjes-alen,' Mededeelingen over Visscherij, Dr P. 

 P. C. Hoek, Helder, 1894, p. 116. 



X Petersen, 4 Das Parungskleid des Aales,' Mittheil. des Deutschcn Seefischereiver- 

 eins, February, 1895. 



