Metamorphosis of the Common Eel. 263 



larva, as well as the hemi-larva, shows a length of body much 

 greater than that exhibited by the young Muraenoid of adult form 

 into which they are transformed. By keeping specimens in an aqua- 

 rium, I was able to establish a diminution of more than 4 cm. during 

 the metamorphosis. With regard to the greatest length which the 

 larva can attain in a given species, -and the amount of diminution 

 which accompanies metamorphosis, there are great individual varia- 

 tions. 



The history of the Common Eel, to which I am now about to 

 refer, is very similar to that given above for the other Mursenoids. 

 The Common Eel (Anguilla vulgaris) undergoes a metamorphosis, 

 and before it assumes the definitive adult form it presents itself as 

 a Leptocephalus, which is known as Leptocephalus Irevirostris. This 

 Leptocephalus was discovered in the Strait of Messina many years 

 ago. A specimen was also captured by the " Challenger," and 

 another specimen was taken by the Zoological Station of Naples in 

 the Strait of Messina. This form is occasionally carried to the 

 surface by currents. By exception, in the month of March, in the 

 year 1895, we captured several thousands of them in one day, but 

 the best way to secure this Leptocephalus (and a very easy one) is to 

 open the intestine of the Orthagoriscus mola, a fish which is common 

 in the Strait of Messina, and in it one is certain to find a very 

 large number of specimens. It must be observed that Orthagoriscus 

 mola is a deep-sea fish. The specimens of Leptocephalus brevirostris 

 found in the intestine of Orthagoriscus are more or less altered by 

 digestion. Those specimens of Leptocephalus brevirostris which are 

 taken near the surface in the open sea are in a better state of preser- 

 vation, but, unfortunately, these also frequently have the epidermis 

 injured so that they cannot maintain their life in an aquarium for 

 more than a few days; they live long enough, however, to allow us 

 to observe that it is their habit to conceal themselves in the sand or 

 in the mud as the Common Eel (Anguilla) does. Here it is to be 

 noted that the various forms of Leptocephali have habits resembling 

 those of the Mursenoids to which they belong, i.e., they dig into the 

 sand or abstain from doing so according as the adult form has or has 

 not this habit. 



I now pass on to the characters of Leptocephalus brevirostris. I give 

 them here in the same order as I shall use in my larger memoir. The 

 length varies from 77 60 mm., the same extent of variation as 

 observed in other Muraenotds. The caudal fin tends to assume the 

 form which it has in the Elver* or young Anguilla. It is to be noted 

 that in other Leptocephali the caudal fin also tends always to exhibit 

 the adult form. The lower jaw projects sometimes more than the 



* The word " Elver " is used in this paper in its strict sense, viz., for the young 

 form of Anguilla vulgaris as taken when ascending rivers in vast numbers. 



