440 THE EEL FAMILY. 



Sennebogen 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 be examined through a microscope, 

 the scales of the females are far smaller than those of the males. 



Petersen has found that very distinct anatomical differences 

 existed between the yellow and silver varieties of eels. ' The 

 sides of the yellow eel are of a canary yellow colour, the back 

 dark grey or brownish black. The 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 the yellow eel be lean, the head appears abnormally 

 large, and the eel has a strange and repugnant appearance. 

 Both males and females are found among yellow eels. 



The silver eels are distinguished by a very striking metallic 

 sheen on the sides and belly. A bronze appearance is often 

 seen in the neighbourhood of the lateral line in females as well 

 as in males. The belly is usually pure silvery white. The 

 eyes of the silver eel are much larger than those of the yellow 

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

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

 seen outside the eyes if the head be looked at from above. The 

 silver eel, according to the fishermen, are always somewhat 

 sharp-headed, are fat and in much favour; the thick-headed 

 speciinens, which are only found among yellow eels, are in poor 

 condition. The sexual organs of the silver eel are more de- 

 veloped, 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 — 38 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 'breeding dress' (Parungs- 

 kleid). This explains why there are no silver females whose 

 total length is less than 42 — 44 cm., and no silver males whose 

 total length is less than 29 — 33 cm., for with those two lengths 

 the two scxe.s become capable of reproduction. The change 

 from the yellow to the silver coloration takes place rapidly — 

 in a few weeks, and at the same time the breast-fins become 



