XIH PHYLUM CHORDATA 323 



Urinary and Reproductive Systems. The kidneys (Figs. 

 986 and 987, k.) are a pair of irregularly shaped, dark red bodies, 

 each consisting of two lobes, anterior and posterior, situated in 

 close contact with the dorsal wall of the posterior portion of the 

 abdominal cavity, and covered with peritoneum on their ventral 

 faces only. Their posterior portions, which are tapering, are in close 

 contact with one another. Each has a delicate duct, the ureter, 

 opening posteriorly into the cloaca. A urinary (allantoic) bladder 

 (bl.), a thin-walled sac, opens into the cloaca on its ventral 

 side. 



In the male the testes (Fig. 986, t.) are two oval white bodies, 

 that on the right side situated just posterior to the right lobe of 

 the liver, that on the left somewhat further back. Each testis is 

 attached to the body-wall by a fold of the peritoneum, the mes- 

 orchium (mso.). The epididymis (ep.) extends backwards from the 

 inner side of each testis, and passes behind into a narrow convoluted 

 tube, the vas deferens or spermiduct (v. d.}, which opens into the 

 terminal part of the corresponding ureter. A pair of vascular 

 eversible copulatory sacs (p, p'.), which when everted are seen to be 

 of cylindrical form with a dilated and bifid apex, open into the 

 posterior p^art of the cloaca. 



In the female the ovaries (Fig. 987, ov.) are a pair of irregularly 

 oval bodies having their surfaces raised up into rounded elevations, 

 marking the position of the ova. They are situated a little further 

 back than the testes, and each is attached to the body-wall by a 

 fold of the peritoneum, the mesoarium (mso.). The oviducts (od.) 

 are thin-walled, wide, plaited tubes which open in front into the 

 cavity of the body (od'.), while behind they communicate with the 

 posterior part of the cloaca, their opening (od".) being distinct from, 

 and a little in front of, those of the ureters. A fold of the peritoneum, 

 the broad ligament (b. lg.), attaches the oviduct to the body-wall. 



2. DISTINCTIVE CHARACTERS AND CLASSIFICATION. 



The Reptilia are cold-blooded Sauropsida (p. 303), with a horny 

 epidermal skeleton of scales, and frequently with an armour of 

 dermal bony plates. The centra of the vertebrae have spheroidal 

 articular surfaces. There are usually only two vertebrae in the 

 sacral region. The episternum, when present, always remains 

 distinct from the clavicles. The floor of the acetabulum is often 

 completely ossified. The pubes and the ischia usually meet in 

 ventral symphyses. The metatarsals do not become ankylosed. 

 The mandible, as well as several bones of the upper jaw, very 

 usually bear teeth. The optic lobes are situated on the dorsal 

 aspect of the brain. The ventricle is rarely divided by a complete 

 partition. There is always a paired aortic arch in the adult. 



