18&6.] OVUM OF OSMERUS EPERLANUS. 293 
which comes into contact with a solid object. The ovum of the 
Smelt is not fixed by the surface of the egg-membrane, but sus- 
pended by a short filament, the distal end of which alone adheres. 
No detailed account seems to have been given of the nature and 
development of the suspending filament. Alex. Agassiz ignores 
altogether the assertions which have been published concerning the 
attacliment of the Smelt-ovum. In his beautiful memoir on Pelagic 
Teleostean Ova, he describes a certain well-characterized pelagic 
ovum, and identifies it as that of Osmerus mordax, Gill. The ovum 
in question, or one exactly similar, has been described by Victor 
Hensen in the ‘ Vierte Bericht der Commission zur Untersuchung der 
Deutschen Meere.’ The most conspicuous charactcristic of this ovum, 
a feature which is unique among the Teleostean ova hitherto described, 
is the segregation of the yolk into polyhedral masses. Agassiz refers 
to this character as the segmentation of the yolk, as if he considered 
the ovum to be holoblastic; but in all probability the subdivision of 
the yolk in this case is similar in nature to the more usual subdivi- 
sion into yolk-spherules, and the polyhedral masses are not cells or 
segmentation-spheres. The same ovum was taken by myself in the 
Firth of Forth in June 1884, and formed the subject of a short 
communication which I made to the Royal Society of Edinburgh. 
If it be true that the ova of Osmerus eperlanus are, during develop- 
ment, fixed to solid objects, it is in the highest degree improbable that 
the ova of Osmerus mordax are pelagic ; and as the adhesive nature 
of the eggs of the British Smelt is beyond all question, the correct 
identification of the peculiar pelagic ovum studied by Hensen, 
myself, and Agassiz is a task for the future. The latest examination 
of the egg of Osmerus eperlanus, before my own work, was made by 
Owsjannikow’, whose results appeared only last year. Owsjannikow 
describes the condition of the ovum when taken from the parent a 
short time before complete maturity has been reached. He makes 
no mention of the attached condition of the deposited ovum, nor of 
the adaptation of the structure of the ripening ovum to the future 
process of adhesion. 
My interest in the ovum of Osmerus having been strongly 
excited by the confusion concerning it, indicated by the literature 
thus summarized, I obtained some living specimens of the fish 
from the neighbourhood of Alloa, in the Forth, and conveyed 
them to my aquarium. I also attempted to fertilize. some ova 
artificially. This experiment was made at the riverside with the 
fish just taken from the seine. As the weather was very cold and 
the water very muddy, little could be made out concerning the ova 
at the time of the experiment. It was seen that very few of the 
ova became attached to the stones on which they were allowed to 
fall. The greater number sank to the bottom of the water, and 
remained quite free ; they became opaque white shortly after expul- 
sion from the fish; at first they are of a translucent yellow 
colour. On examining them next day in the laboratory, I found they 
1 “Studien iiber das Hi, hauptsachlich der Knochenfische,” Mémoires de l’Aca- 
démie Impériale de St. Pétersbourg, 1885. 
