164 FISHES. 



the Batrachian type. The ovaries are not closed, except in 

 Lepidosiren ; all Ganoids possess oviducts. In the Sturgeons 

 the oviduct as well as the vas deferens is represented by 

 a funnel-shaped prolongation of the peritoneum, which com- 

 municates with the wide ureter. The inner aperture of 

 the funnel is on a level of the middle of the testicle or 

 ovary, the outer within the ureter ; and it is a noteworthy 

 fact that only at certain periods of the life of the fish this 

 outer aperture is found to be open, — at other times the peri- 

 toneal funnel appears as a closed blind sac within the ureter. 

 The mode of passage of the semen into the funnel is not known. 



In Polypterus and Amia, proper oviducts, with abdominal 

 apertures in about the middle of the abdominal cavity, are 

 developed ; they coalesce with the ureters close to the com- 

 mon urogenital aperture. 



In Ceratodus (Fig. 77), a long convoluted oviduct extends 

 to the foremost limit of the abdominal cavity, where it opens 

 by a slit at a considerable distance from the front end of the 

 long ovary ; this aperture is closed in sexually immature speci- 

 mens. The oviducts unite close to their common opening in 

 the cloaca. During their passage through the oviduct the ova 

 receive a gelatinous covering secreted by its mucous mem- 

 brane. This is probably also the case in Zepidosiren, which 

 possesses a convoluted oviduct with secretory glands in the 

 middle of its length. The oviduct begins with a funnel- 

 shaped dilatation, and terminates in a wide pouch, which 

 posteriorly communicates with that of the other side, both 

 opening by a common aperture behind the urinary bladder. 



The ova of Ganoids, as far as they are known at present, 

 are small, but enveloped in a gelatinous substance. In the 

 Sturgeon have been counted as many as 7,635,200. Those 

 of Zepidosteus seem to be the largest, measuring 5 millimetres 

 in diameter with their envelope, and 3 millimetres without 

 it. They are deposited singly, like those of Newts. 



