EGGS AND LARVAE OF TELEOSTEANS. 107 



long been known, but all attempts to trace it with certainty into connection 

 with a particular species of fish have hitherto failed. The eggs and larvae 

 were first described by A. Agassiz* in 1882, under the name Osmerus mordax, 

 Gill, figures being given of the newly hatched larva and some older stages. 

 Agassiz appears to have obtained his figures of the later stages from specimens 

 taken in the tow-net, not from larvae reared in captivity directly from the egg. 

 He states that at first he supposed the larvae to belong to some Clupeoid species, 

 until he saw a paper by Mr H. J. Eice, on the development of Osmerus, when 

 he became convinced that his specimens were really to be ascribed to Osmerus 

 mordax. He points out that the oldest larva he figures has a striking 

 resemblance to Scombresox and Belone. As a matter of fact this resemblance is 

 not very exact, and as it is known that the eggs of all the Scombresocidw are 

 provided with filamentous processes of the vitelline membrane, it is certain that 

 the ovum under consideration cannot belong to any member, of that family. 

 Agassiz also remarks that the resemblance of the development of Osmerus to 

 that of the herring as given by Sundevall t is very close. Now Sundevall 

 gives a figure of the larva of Osmerus eperlanus, which shows an oil globule in 

 the yolk sac, and I have shown that the ovum of O. eperlanus is adhesive. Thus 

 it is impossible that Agassiz' larva should be that of Osmerus mordax. Two 

 species of the same genus could not differ so greatly in the structure of their 

 ova and the conditions to which those ova are exposed, as do the pelagic ovum 

 we have been considering, and the ovum of Osmerus eperlanus. Moreover, 

 Osmerus mordax does not occur in the British seas. It is certain that the 

 herring cannot be the parent of the ovum in question, in spite of the resem- 

 blance between the larva derived from it and the herring larva, for the ova of 

 the herring are well known, and are not pelagic. This same pelagic ovum and 

 larva have been described by V. Hensen,J and that gentleman, courteously 

 replying to inquiries of mine on the subject, said, in his opinion, the parent 

 species was the sprat. But here we have the same difficulty as in the case of 

 Osmerus. Can any species of Clupea have pelagic ova? No instance is yet 

 known of a typically adhesive and a typically pelagic ovum occurring in the 

 same genus. Nevertheless the segregation of the yolk in our pelagic ovum is 

 not altogether incomparable with the condition of the yolk in the herring. It 

 seems absolutely certain that the problematic ovum belongs to some physosto- 

 mous fish, but hitherto no physostomous fish is known to have a pelagic ovum. 

 It has struck me as possible that the parent we are seeking to discover is really 

 the eel, Anguilla vulgaris. At all events the fertilised spawn of the eel has 

 never been examined. 



* Young Stages, pt. iii. f Svensk. Vetensk. Akad., 1855. 



% Vierter Ber. Com. Unt. Deutsches Meere, Berlin, 1883. 



