966 GENERATIVE APPARATUS. 



the abdomen with the blood-vessels) ; they form a small particular plexus around 

 the artery. (The nerves pierce the membrana propria of the tubuli semiuiferi, 

 and end in a more or less pyramidal mass of protoplasm, in which lie clear 

 elliptical nuclei. The ends of the fibres, therefore, lie in close proximity to the 

 outer layer of the secreting cells.) 



Development. — In the foetus, at an early age, the testicle floats in the 

 abdominal cavity, being suspended from the sublumbar region, near the flank, 

 by a wide peritoneal fold, at the anterior border of which are the spermatic 

 vessels (Fig. 520, e) ; the tunica vaginalis is not yet present. The mechanism 

 of the formation of this is very simple, and easy to understand. The visceral 

 layer of the tunica vaginalis, Avhich envelops the testicle and the cord, being 

 already formed, as well as the serous frienum that establishes continuity between 

 this and the parietal layer in the adult animal, it only remains to explain how nature 

 proceeds to construct the vaginal sac in which the gland is afterwards contained. 



We have remarked that to the posterior extremity of the testicle is attached 

 a thick round funicle, the other end of which passes into the internal inguinal 

 ring ; this is enveloped by the peritoneum, and fixed to the posterior border of 

 the serous layer that suspends the testicle. This funicle is the guhernaadum 

 testis, and is continuous by its inguinal extremity with the dartos, the structure 

 of which it apparently shares, and which alone acts as the scrotal sac to it. 

 The serous layer covering it has on its outer adherent face the cremasteric muscle, 

 which is attached to the ilio-lumbar aponeurosis in the vicinity of the inguinal 

 ring, enters the serous tube formed by the peritoneal envelope of the guberna- 

 culum, and advances by its terminal extremity to near the testicle. To this 

 organ is due the principal share in the formation of the vaginal pouch. 



When the progress of development in the foetus pushes the testicle towards 

 the inguinal region, the gubernaculum acts as a guide, as its picturesque name 

 sufficiently indicates. It is the first to descend into the inguinal opening, draw- 

 ing the testicle after it. But in performing this movement it also carries along 

 its peritoneal covering, which gradually leaves it to become related, by its 

 adherent face, to the walls of the inguinal canal ; and thus this membrane 

 becomes reflected, just as would a sock everted or turned down from the leg ta 

 the foot, the latter being supposed to represent the testicle. 



The parietal layer of the vaginal sac is, then, nothing more than the serous 

 tube that, in the foetus, enveloped the gubernaculum testis while it was in the 

 abdomen, and which is reversed on the testicle and cord after their descent into 

 the scrotum, the cremasteric muscle on its adherent face having become external. 



In all species, the descent of the testicle commences before birth : in the 

 Bovidfe it is even completed in the early months of intra-uterine existence. In 

 Solipeds, however, the testicle most frequently remains in the inguinal canal 

 until the animal is from six to ten months old. 



Function. — The testicles secrete the spermatic (or seminal) fluid. Pure semen, 

 such as is derived from these glands, is a white, viscid, odourless, and slightly 

 alkaline fluid. It contains a small quantity of liquid matter (Uqiior seminis), 

 in which is an innumerable mass of spermatozoids. After the semen has passed 

 through the genital canals, it is made much more watery by the addition of 

 the fluids secreted by the walls of these excretory ducts, or by the glands annexed 

 to them. 



The spermcdozon, zoosperma, spermatozo'ides, or spernwtic filaments, are little 

 elongated bodies from gio to sU of a line in length. They have a pyriform, 



