844 Proceedings of the Boy at Physical Society. 



each side is a raised band covered by an epithelium, which 

 is somewhat thick but not germinal. From the mediad 

 side of this band projects a thick and deep fold, bearing on 

 its outer side a germinal mass of young ova ; from the ex- 

 ternal side of the band is a much smaller fold, which contains 

 no young ova; the edges of these two folds coalesce, and 

 thus the tubular ovary is formed. 



In the posterior part of the body cavity, long before the 

 point is reached where that cavity is divided into its two 

 ultimate prolongations, all trace of the generative organs dis- 

 appears. In tracing back the ovarian folds they are seen to 

 become smaller and smaller, until they cease altogether. After 

 the folds are no longer visible, the pair of slightly thickened 

 bands in the wall of the body cavity can still be recognised, 

 though they are not prominent, and farther back these also 

 disappear altogether, and no further trace of ovary or oviduct 

 can be seen. One peculiarity seen in a series of sections of 

 the sprat deserves to be mentioned. The urinary vesicle does 

 not extend forward in front of the point where the segmental 

 ducts open into it, as is the case in most fishes ; in the more 

 anterior region of the body is seen a large tube between the 

 kidneys and the body cavity ; this is the large air-bladder, 

 which passes backwards to open to the exterior behind the 

 anus on the left side. In sections a little in front of the 

 anus the urinary vesicle and the air-bladder are seen side by 

 side. 



I have made some attempts to trace the history of the 

 coalesced ovaries of Zoarces vivipa'incs, but without much 

 success. In the young Zoarces 4*5 cm. long taken from the 

 mother, but ready to be born, the ovary is already a single 

 tubular organ, and there is no indication of its origin from 

 two separate rudiments. Moreover it is enclosed in the 

 mesentery, and removed from the wall of the body cavity, no 

 indication being visible of its original position. The tube 

 ends blindly behind, near the level of the anterior limit 

 of the urinary vesicle, and there is no trace or sign of the 

 formation of a duct by which the tubular ovary could open to 

 the exterior. No air-bladder is present. 



In other specimens which had been kept alive six weeks 



