Page:Proceedings of the Royal Society of London Vol 60.djvu/289

Rh larva, as well as the hemi-larva, shows a length of body m uch greater than th a t exhibited by the young Muraenoid of adult form into which they are transform ed. By keeping specimens in an aquarium, I was able to establish a dim inution of more than 4 cm. during the metamorphosis. W ith regard to the greatest length which the larva can attain in a given species, and the am ount of dim inution which accompanies metamorphosis, there are great individual variations.

The history of the Common Eel, to which I am now about to refer, is very sim ilar to th a t given above for th e other Murtenoids. The Common Eel ( Anguilla vulgaris) undergoes a m etam orphosis, and before it assumes the definitive adult form it presents itself as a Leptocephalus, w hich is know n as brevirostris. This Leptocephalus was discovered in the S trait of Messina m any years ago. A specimen was also captured by the “ C hallenger,” and another specimen was taken by the Zoological Station of Naples in the S trait of Messina. This form is occasionally carried to the surface by currents. By exception, in the m onth 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, 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 viola is a deep-sea fish. The specimens of Leptocephalus brevirostris found in the intestine of O rthagoriscus 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 preservation, but, unfortunately, these also frequently have the epidermis injured so that they cannot m aintain th eir 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 (A nguilla) does. H ere it is to be noted that the various forms of Leptocephali have habits resem bling 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.

1 now pass on to the characters of Leptocepha brevirostris. I give them here in the same order as I shall use in my larger memoir. The length varies Irom 77 60 mm., th e same extent of variation as observed in other Muraenoids. The caudal fin tends to assume the form which it has in the Elver* or young Anguilla. I t is to be noted t nit 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 m ot Anguilla vulgaris as taken when ascending rivers in vast numbers.