Page:Proceedings of the Royal Society of London Vol 60.djvu/288

262 Therefore, the hypothesis of G unther th a t the Leptocephali are abnormal larvas, incapable of fu rth er development, m ust be rejected. All this is related by m yself at length, w ith all historical details which concern the question, in a large memoir which is about to appear in the Journal edited by Professor Todaro.

Until now all these facts have been unknown because normally they can only be observed in the abysses of the sea at a depth of at least 500 metres. Fortunately, along a p art of the coast of Sicily strong currents occur, which m ust be ascribed to the tide, producing very large displacem ents of the w ater in the narrow S trait of Messina. I shall give further details concerning these currents in my large memoir. In consequence of the strong currents, sometimes—I say sometimes, because there is no regularity, and one may have to wait for a year w ithout obtaining any m aterial— not only many deep-sea fishes, b u t also all stages of the development of the Muraenoids are m et w ith in the surface-w ater. To these currents we owe all the captures of Murcena helnawith ripe eggs, which is in accordance w ith w hat I had already argued from other facts, namely, that the reproduction of the Muramoids takes place at great depths of the sea.

Before I proceed to speak of the Common Eel, I m ust premise that Dr. Raffaele has described certain pelagic eggs as belonging to an undeterm ined species, putting forw ard the suggestion that these eggs belong to some Mursenoid. This m atter has been investigated by myself, and I have shown th at the newly hatched larvae (called “ prae-larvae ” by me) derived from these eggs have essentially the character of Leptocephali.

The life history of the Muraenoids, leaving aside for the present the Common Eel, is as follow s:— Females can only m ature in very profound depths of the sea, th at is to say, at least a depth of 500 m etres. This fact I established by finding well-known deep-sea fishes together w ith Leptocephali, ripe Murmnse, and quite ripe eels (see below). The females of those species which do not live at this depth m ust therefore m igrate to it. The male, however, can m ature at a smaller depth, and therefore they m igrate into the greater depth when they are already m ature. Fertilisation takes place at great d ep th s; the eggs float in the w a te r; nevertheless they remain at a great depth in the sea, and only exceptionally, for unknown reasons, some of them m ount to the surface.

From the egg issues rapidly a prae-larva, which becomes a larva (Leptocephalus) w ith the anus and the urinary opening near the tip of the tail. The larva then becomes a hemi-larva, the two apertures just named moving their position towards the anterior part of the body, which becomes thickened and nearly round. By further change the hemi-larva assumes the definitive or adult form. e