46 REPORT OF COMMISSIONERS OF INLAND FISHERIES. 



The scientific investigation of the eel question dates from 1777, 

 when Mondini published a paper which gave an excellent description 

 of the ovary of the female eel. The further account of the long and 

 difficult search into this baffling subject is not less humanly inter- 

 esting than scientifically important, but its details can not be given 

 here. Jacobyf has adequately and interestingly related the history 

 of the earlier investigations. Here it is suflEicient merely to mention 

 the discovery of the testes of the eel, which was made by Syrsky no 

 longer ago than 1873. This discovery was important because it 

 established the fact that the mature male eel is much smaller than 

 the mature female, but more particularly because it refuted the 

 theory that eels are complete hermaphrodites, which up to that 

 time had been supported by a considerable weight of authority. 



The next important advance in our knowledge of the natural 

 history of the eel was made by Raffaele, in 1888, who described five 

 species of pelagic fish eggs secured during the months from August 

 to November in the Gulf of Naples. These eggs, on account of the 

 character of the larvae they produced, he referred to different species 

 of eels. This was the first description of the developing egg and 

 early larvae of any species of the eel family. 



This left an important hiatus in our knowledge of the life history 

 of the eel. The development of the larvae after about the fifth day 

 from hatching was entirely unknown, and there was no means of 

 identifying the eggs and larvae with particular adult forms. This 

 gap in our knowledge did not long remain, however, for a little later 

 Grassi and Calandruccio, in their epoch-making work on the develop- 

 ment of the eels, identified Raff aele's egg No. 10, without oil globules 

 with a diameter 2.7 mm, with that of the common eel. They also 

 showed the true character of Raffaele's newly hatched larvae by 

 identifying them with certain forms which had long been known to 

 science under the name Leptocephali. These forms had previously 

 been a puzzle to naturalists. When first discovered (1763) they 

 seemed to present such radical differences from any adult form that 



t Report U. S. Fish Commission, 1879. 



