68 SCIENCE FROM AN EASY CHAIR 



and broad-nosed eels (probably males and females). The 

 remarkable fact, admitted by both fishermen and anatom- 

 ists, was that you could not really tell male from female, 

 nor, indeed, ever find an eel (that is, a common eel, as dis- 

 tinguished from the much larger and well-known conger 

 eel) which was ripe, or, indeed, showed any signs of having 

 either roe or milt within it. A popular legend exists that 

 eels are produced by the " vivification " of horse-hair. Occa- 

 sionally in summer a long, black, and very thin thread- 

 worm (called Gordius by naturalists) suddenly appears in 

 great numbers in rivers, and these are declared by the 

 country-folk to be horse-hairs on their way to become eels ! 

 I remember a sudden swarm of them one summer in the 

 upper river at Oxford. Really, they are parasitic worms 

 which live inside insects for a part of their lives, and leave 

 them in summer, passing into the water. Fanciful beliefs 

 about aquatic creatures are common, because it is not very 

 easy to get at the truth when it is not merely at the 

 bottom of a well but at the bottom of a river or of the 

 deep sea ! The fishermen of the east coast of Scotland, 

 who think very highly of their own knowledge and in- 

 telligence, believe that the little white sea-acorns or rock- 

 barnacles are the young of the limpets which live side by 

 side with them, and are scornful of those who deny the 

 correctness of what they consider an obvious conclusion ! 



A few years ago the Scandinavian naturalist, Petersen, 

 showed that the " silver " eels are a later stage of growth 

 of the "yellow" eels ; that they acquire a silvery coat, and 

 that the eye increases in size as a sort of "wedding 

 dress," just before they go down to the sea to breed. I 

 owe to Petersen's kindness the coloured drawings of the 

 heads of the yellow and the silver eel reproduced in 

 Plate I. These silver eels are caught in some numbers 

 about the Danish coast and river mouths, moving down- 

 wards ; and Petersen has been able to distinguish the 



