18^(i.] OVUM OF OSMERUS El'ERLANUS. 293 



which comes info contact with a sohd object. The ovum of tlie 

 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 accovint seems to have been given of tlie 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 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 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 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, httle 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 thev 



' " Studien iiber das Ei, hauptsachlich der Knoelienfische," Mernoiras de I'Aca- 

 demie Imp^riale dp St. P6tprsbonrg, 1885. 



