79 
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. pp.) 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 ccelomiec, 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 externally, 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, xxxy., pt. 3, No. 19, 
