xiii PHYLUM CHORDATA 165 



abdominal cavity. In front the two unite behind the pericardium 

 to open into the abdominal cavity by a wide median aperture 

 (ovd'.). At about the point of junction of the middle and 

 anterior thirds is a swelling marking the position of the shell- 

 gland (sh. gl.) The posterior part dilates to form a wide 

 uterine chamber, and in Scyllium the two unite to open into 

 the cloaca by a common aperture situated just behind the 

 opening of the rectum, while in Hemiscy Ilium' they remain distinct 

 and have separate cloacal openings. Each kidney consists of two 

 parts, anterior and posterior. The former (Fig. 817, r. meson, 

 Fig. 824, k') is a long narrow ribbon of soft reddish substance, 

 which runs along throughout a great part of the body-cavity at 

 the side of the vertebral column, covered by the peritoneum. 

 The posterior portion {r. metan, k) is a compact, lobulated, dark- 

 red body, lying at the side of the cloaca, continuous with the 

 anterior portion ; like the latter it is covered over by the peritoneum. 

 Both portions have their ducts. Those of the anterior are narrow 

 tubes, which run over its ventral surface and become dilated behind 

 to form a pair of elongated chambers, the urinary sinuses (Fig. 825, 

 ur. sin.), uniting behind into a median sinus {med. ur. sin.), 

 opening into the cloaca by a median aperture situated on a papilla, 

 the urinary pajiilla. The ducts of the posterior portion, the 

 ureters, which are usually from four to six in number, open into the 

 urinary sinuses. 



In the male (Fig. 824) there are two elongated, soft, lobulated 

 testes, each attached to the wall of the abdominal cavity by a fold 

 of peritoneum — the mesorchium. From each testis anteriorly, a 

 small number of efferent ducts pass to the anterior end of a long, 

 narrow, strap-shaped body, which corresponds to the vestigial 

 anterior portion of the kidney in the female. This is the epi- 

 didymis ; the duct, spermiduct or zas deferens, runs along the entire 

 length of the non-renal part of the kidney, or " Leydig's gland," 

 and, where it leaves the latter posteriorly, becomes a wide tube, 

 which opens into the urinogenital sinus (?4. g. s.), a median chamber 

 projecting into the cloaca. Posteriorly the spermiduct dilates to 

 form a wide thin- walled sac, the vesicula seminalis. Closely applied to 

 the latter is a thin-walled elongated sac, the sperm-sac. Anterioly 

 the sperm-sac narrows to a blind extremity ; posteriorly the right 

 and left sperm-sacs combine to form the urinogenital sinus. The 

 posterior part of the kidney has the same character as in the 

 female; its ducts, usually five in number on each side, open into 

 the urinogenital sinus, some of the most anterior first uniting to 

 form a common tube. The sinus has a median aperture into the 

 general cavity of the cloaca situated on the summit of a prominent 

 v/rinogenital papilla. The oviducts (Miillerian ducts) of the 

 female are represented in the male by vestiges of their anterior 

 portions {m.d). The entire kidney is sometimes regarded as a 



