57 



cavity. TJVHien the intestines are lifted up or removed, tlie riglit testis is seen, a 

 triangular flat solid mass about 8 mm. broad at its posterior end, aiid 13 mm. long, 

 lying at the anterior end of the right lateral bod)^ cavity, close to the front edge of the 

 skeletal partition to which its inner surface is attached. 



On the left side there is no left lateral body cavity, but the posterior portion of the 

 fused renal organs extends backwards between the lateral muscle and the skeletal 

 partition : this part of the kidney is as large in proportion as in the female, and has the 

 same relations to the urinary bladder. 



The left testis is only about half the size of the right. In this specimen it was 4 mm. 

 broad above, and 10 mm. in length. The right testis is somewhat flat, and its greatest 

 length is nearly antero-posterior in direction ; the left has the form of a triangular 

 pyramid with its point downwards, and its greatest length is dorso-ventral in direction. 

 The left testis is situated in the main body cavity attached to the peritoneum over the 

 surface of the kidney by a membrane, the mesorchium. 



From the apex of each testis passes off" the vas deferens or duct by which the milt 

 or semen is conveyed to the exterior. Each vas deferens contains not a single cavity 

 but several, and it is attached to the anterior surface of the urinary bladder. The 

 vasa deferentia being translucent are not conspicuous ; their external aperture is at 

 the end of a small papilla on the right side, which is pierced also by the terminal 

 part of the urinary duct. Thus in both sexes there is a papilla on the right side ; in 

 the female it is a urinary papilla, in the male it is urinogenital. In the figure the 

 wooden rod is inserted through the anus into the end of the rectum, while the black 

 bristle passes into the urinary bladder the walls of which are exceedingly transparent 

 and indistinct, especially when the bladder is empty and collapsed. 



Thus the male organs of reproduction in the sole are extraordinarily small in 

 proportion to the size of the body. In other flat fishes, 'e.g., the plaice, PI. platessa, or 

 merry sole, Fl. microcejy/ialus, they are smaller than the ovaries, it is true, but many 

 times larger than those of the sole, and in the breeding season they become enlarged 

 and soft, and of a milk-white colour. In this condition they at once attract notice 

 when a male fish is cut open. In the sole, on the contrary, although the testes beiiome 

 slightly enlarged during the spawning period, they become neither white, nor soft, 

 nor conspicuous. In fact they are not known to the fisliermen, who are unable to 

 recognise in the small yellow organs of the sole the male reproductive organs 

 which they usually find in other fishes as large, white, soft, and conspicuous 

 masses. The testes of the sole are, moreover, completely concealed beneath the 

 intestine. Until recently even ichthyologists were for the most part unacquainted 

 with the structure and relations of the male organs of the sole. In the 

 Fifth Annual Eeport of the Fishery Board for Scotland, p. 233, it is stated that " the 

 hatching of the sole, e.g., presents this one great difficulty, that males are rarely ever 

 captured, or, at least if captured, are seldom identified." As a matter of fact males 



