580 ANATOMY OF VERTBBKATES. 



form than in other Reptiles. In the common harmless Snake 

 ( Coluber natrix) they are oblong, subcompressed, in advance of the 

 Isidneys, the right about an inch more forward than the left, 

 corresponding to the difference in the relative position of the 

 kidneys. In the Rattlesnake the testes arc more symmetrical 

 in position. The vas deferens, disposed in short undulations, 

 goes along the kidney to the cloaca, the papillas terminating near 

 the beginning of the urethral groove. The intromittent organs 

 are two in number, and consist of invertible sheaths, or long 

 narrow bags, with a highly vascular papillose lining membrane, 

 bifurcate at their blind end, to which are attached the muscles, 

 fig. 357, I, for inverting and keeping them retracted and hidden 

 in the base of the tail. By tumefaction of the vascular portions 

 of the bags, and the action of the ' constrictor basis caudte ' and 

 ' sphincter cloaca^,' they are everted. In the Rattlesnake the 

 blind end of each inverted pouch bifurcates, and the vascular 

 membrane is thickened and produced into many processes near 

 the bifurcation : when eversion with erectile tumefaction of the 

 parts takes place, each penis presents a papillose and bifurcate 

 glans, as in fig. 357, k. In Elaphis quadrilineatus the body of 

 the penis presents large retroverted papilla3, and the glans is 

 beset with small flattened wrinkled processes. 



In the Slow-worm (^Anguis) the testes are situated a little 

 anterior to the dilated rectum, the right in advance of the left ; 

 the sperm-duct simulates a long epididymis by its initial convolu- 

 tions or transverse folds. The intromittent organs are invertible 

 and evertible pouches, as in Serpents, but are shorter. 



In a Scinc-lizard ( Tiliqua) the right testis is more advanced 

 in position than the left. The body of the penial pouch, when 

 everted, shows transverse rugte, and the sub-bifurcate glans short 

 retroverted papillaj. In Lacerta ocellata, as in Draco volans, 

 fig. 389, the testes, b, show a similar degree of unsymmetrical 

 position. The sj)erm-ducts form, by a series of short transverse 

 folds, a long body or band, like an epididymis : but there is no 

 structure properly so called consisting of the convolutions of 

 several efferent tubes prior to their union to form the vas 

 deferens, ib. e. In the interspace of the orifices of the ureters 

 a ridge is continued backward, on each side of which is the orifice 

 of the vas deferens, whence is continued the urethral groove 

 extending along the penial sheath to the papillose blind end or 

 glans. 



The peritoneal covering of the testes shows in some Lizards 



