594 REPRODUCTION. 



quadrupeds, or if subjected to extremes of heat or cold, the motion of 

 the spermatozoa ceases, and they soon disintegrate. 



Formation of the Spermatozoa. The testicles, within which the 

 spermatozoa are produced, are the characteristic organs of the male 

 sex, as the ovaries are characteristic of the female. In man and mam- 

 malia, they are solid, ovoid-shaped bodies, composed mainly of long, 

 narrow, convoluted tubes, the " seminiferous tubes," lying for the most 

 part closely in contact with each other, and separated only by capillary 

 blood-vessels and a little connective tissue. The seminiferous tubes 

 commence, by rounded extremities, near the external surface of the 

 testicle and pursue an intricately convoluted course toward its central 

 and posterior part. They are not strongly adherent to each other, and 

 may be readily unravelled by manipulation. 



According to Kolliker, the formation of the spermatozoa takes place 

 within peculiar cells occupying the cavity of the seminiferous tubes. 

 As puberty approaches, beside the ordinary pavement epithelium lining 

 the tubes, larger cells make their appearance, each containing from one 

 to twenty nuclei, with nucleoli. In these cells the spermatozoa are 

 formed ; their number corresponding usually with that of the cell- 

 nuclei. They are developed in bundles, held together by the mem- 

 branous envelope surrounding them, but are afterward set free by 

 the liquefaction of the cell-wall, and mingled with a small quantity of 

 transparent fluid. 



While in the seminiferous tubes, the spermatozoa remain inclosed in 

 their parent vesicles; they are liberated, and mingled together, only 

 after entering the rete testis and the head of the epididymis. 



Accessory Male Organs of Generation. Beside the testicles, there 

 are certain accessory organs by which the spermatic fluid is conveyed 

 to the exterior, and mingled with various secretions which assist in the 

 accomplishment of its function. 



As the spermatozoa leave the testicle, they are crowded together in 

 an opaque, white, semi-fluid mass, which fills the vasa efferentia, and 

 distends their cavities. It then enters the single duct forming the body 

 and lower extremity of the epididymis, following the tortuous course 

 of this tube, until it reaches the vas deferens, by which it is conveyed 

 to the vesiculae seminales. Throughout this course it is mingled with 

 a scanty mucus-like fluid, secreted by the epididymis and vas deferens. 

 The vesiculae seminales also contain a fluid secretion, which serves 

 some secondary purpose in completing the formation of the sperm. 

 One of its functions is no doubt to dilute the mass of spermatozoa, 

 and give them liberty of motion ; as well as to increase the volume 

 of the spermatic fluid, and thus enable it to be expelled by the mus- 

 cular contraction of the parts about the urethra. Kolliker has found 

 the spermatozoa in the vas deferens and epididymis generally quiescent ; 

 their motion being exhibited only in the vesiculae seminales and in the 

 ejaculated sperm. 



At the moment of its evacuation, the sperm first passes from the 



