348 FISHES 



of the carp. It has been shown for the plaice and cod and 

 some other fishes that the otoliths give more distinct indications 

 than the scales. The otolith is a concretion of carbonate of lime 

 formed in the vesicle of the auditory organ ; the deposit formed 

 in summer is opaque while that formed in the latter part of the 

 year is more transparent so that each double zone of white and 

 transparent substance represents one year of age. By this 

 method it has been found that in the plaice the males not only 

 become mature at least a year earlier than the females but die 

 at an earlier age, all the specimens above six or seven years of 

 age being females. Some few fishes appear to be annual, 

 emerging from the egg, attaining maturity and dying within 

 one year ; this is stated to be the case for Crystallogobius nillsoni 

 which occurs in abundance at depths between twenty and thirty 

 fathoms off the south coast of England and the south and 

 west of Ireland. 



Life-history of Eels 



The natural history of the eel possesses a special interest and 

 deserves separate consideration. It is remarkable that the re- 

 production of so common an animal should have remained an 

 inexplicable mystery from the time of Aristotle until the last 

 few years. And while professional naturalists were until lately 

 unable to trace out the life-history, imaginary explanations of its 

 origin were invented. Aristotle stated that eels arose from 7/79 

 evrepa, literally meaning the entrails of the earth, but the term 

 has been explained as meaning simply earthworms, while the 

 band-like larvae known as Leptocephali, now known to be the 

 young stages of eels, are known to the fishermen of Palermo as 

 lombrici or vermicelli di mare, worms of the sea. It is therefore 

 suggested that the marine larvae of the eel were not unknown 

 to Aristotle, but it is evident that the chain of reasoning on 

 which the suggestion depends is exceedingly slender, and is 

 not worth serious consideration. At Catania the Leptocephali 

 are called morenelle, which means little Muraenas. 



The family of eels contains a large number of genera and 

 species inhabiting the sea and fresh waters in different parts of 

 the globe. In this country only two species are common, the 

 fresh-water eel and the marine conger. In adult specimens of 

 either species, the generative organs are usually very incon- 



