THE STORY OF THE COMMON EEL 69 



males from the females by finding the still incompletely 

 formed milt and roe within the silver eels. Not only that, 

 but one of Petersen's assistants at the Danish Biological 

 Station has found that you can tell the age of an eel by 

 the zones or rings shown by its scales, when examined 

 with a microscope, just as the age of trees can be told by 

 the annual rings of growth in the wood. Most people, 

 even if familiar with eels, even cooks who have skinned 

 an eel, do not know that they have scales ; but they have, 

 very small ones. The age of other fishes has been 

 similarly ascertained by annual zones of growth marked 

 on the scales ; and lately the age of plaice has been found 

 to be conveniently given by zones of growth formed 

 annually on the little ear-stones which we find in the 

 liquid-holding sac of the internal ear. I am afraid many 

 of my readers will be surprised to learn that fishes have 

 an internal hearing apparatus similar to our own, also that 

 they have olfactory organs, and, in some cases, a well- 

 grown tongue! 



The power thus obtained of telling the age of an eel 

 has led to the following knowledge about them, namely, 

 that female eels do not become " silver " eels and " run 

 down" before they are seven years old, and often not 

 till eight and a half years of age, or even sometimes 

 eleven or twelve years, when they are nearly 3 feet long. 

 The male eel becomes " silver " (instead of " yellow ") at 

 an earlier age four and a half years, and rarely defers 

 his nuptial outburst until he is seven or eight years old. 

 The females of the same age are larger than the males ; 

 a usual size for silver females of seven years old is a little 

 over 2 feet, and of a silver male of the same age 20 inches. 



The further facts which I am about to relate as to the 

 migration and reproduction of the common eel are of 

 great interest. The common " yellow " eels of our ponds 

 and rivers, as we have seen, when they are from five to 



