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Show 1886.] 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 suspended 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 attachment 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 morclax, Gill. The ovum in question, or one exactly similar, has been described by Victor Hensen in the ' Vierte Benefit der Commission zur Untersuchung der Deutschen Meere.' The most conspicuous characteristic 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 subdivision 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 development, fixed to solid objects, it is in the highest degree improbable that the ova of Osmerus morclax 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 Owsjannikow1, 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. M y 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 m y 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 expulsion 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 fiber das Ei, hauptsachlich der Knochenfische," Memoires de l'Aca-demie Imperialc de St. Petersbourg, 1885. |