SEA-FISHERIES LABORATORY. 223 



terior surface of the kidney between the paired terminal 

 processes into which the genital veins open. It is a single 

 tube which immediately on entering the kidney divides 

 to form the paired segmental (or Wolffian) ducts which 

 traverse the entire length of the organ. The ureter 

 rapidly expands into the urocyst (urinary bladder), a large 

 thin walled sac lying between the ovaries (or testes) in 

 front of and rather to one side of axonost 1. Its most 

 expanded portion is near the rectum. Its cavity then 

 rapidly diminishes, and the efferent ureter is a tube with 

 an extremely contracted lumen. It passes to the right 

 side and runs forwards in the dense connective tissue of 

 the body wall, surrounding and posterior to the anus. It 

 then curves laterally at a sharp angle and opens externally 

 on to the surface through the urinary papilla. The latter 

 (Ur. jjj).) is an unpaired prominent projection of the body 

 wall to the right side and immediately posterior to the anus. 



Detailed observations of the development of the 

 Teleostean urocyst are few, but it seems most probable 

 that it is of hypoblastic origin, and that its cavity, unlike 

 that of the segmental duct, which is ccelomic, is really a 

 cloacal portion of the hind gut. Mcintosh and Prince* 

 give a description of the early condition of the vesicle in 

 Molva, though its origin or latter fate is not described. 

 In the youngest plaice (one week after hatching) of which 

 we have made serial sections the united segmental ducts 

 appear to open into the hind gut, which does not yet open 

 to the exterior. In plaice a fortnight old the hind gut 

 opens external^, and the urocyst ceases to have any connec- 

 tion with its cavity, but opens independently in the middle 

 ventral line of the body immediately behind the anus. 



The secretory tissues of the kidney are the uriniferous 



* Development and Life Histories of Teleostean Fishes. Trans. Roy. 

 Soc, Edinburgh, vol. xxxv., pt. 3, No. 19. 



