MALE OKGANS OF GENERATION. 559 



In order to preserve their vitality, the spermatozoa must be 

 kept at the ordinary temperature of the body, and preserved 

 from the contact of the air or other unnatural fluids. In this way, 

 they may be kept without difficulty many hours for purposes of 

 examination. But if the fluid in which they are kept be allowed 

 to dry, or if it be diluted by the addition of water, in the case of 

 birds and quadrupeds, or if it be subjected to extremes of heat or 

 cold, the motion ceases; and the spermatozoa themselves soon begin 

 to disintegrate. 



The spermatozoa are produced in certain glandular-looking 

 organs, the testicles, which are characteristic of the male, as the ova- 

 ries are characteristic of the female. In man and all the higher 

 animals, the testicles are solid, ovoid-shaped bodies, composed 

 principally of numerous long, narrow, and convoluted tubes, the 

 " seminiferous tubes," somewhat similar in their general anatomical 

 characters to the tubuli uriniferi of the kidneys. These tubes lie 

 for the most part closely in contact with each other, so that nothing 

 intervenes between them except capillary bloodvessels and a little 

 areolar tissue. They commence, by blind, rounded extremities, near 

 the external surface of the testicle, and pursue an intricately con- 

 voluted course toward its central and posterior part. They are not 

 strongly adherent to each other, but may be readily unravelled by 

 manipulation, and separated from each other. 



The formation of the spermatozoa, as it takes place in the 

 substance of the testicle, has been fully investigated by Kolliker. 

 According to his observations, as the age of puberty approaches, 

 beside the ordinary pavement epithelium lining the seminiferous 

 tubes, other cells or vesicles of larger size make their appearance 

 in these tubes, each containing from one to fifteen or twenty nuclei, 

 with nucleoli. It is in the interior of these vesicles that the sper- 

 matozoa are formed ; their number corresponding usually with that 

 of the nuclei just mentioned. They are at first developed in bundles 

 of ten to twenty, held together by the thin membranous substance 

 which surrounds them, but are afterward set free by the liquefac- 

 tion of the vesicle, and then fill nearly the entire cavity of the 

 seminiferous ducts, mingled only with a very minute quantity of 

 transparent fluid. 



In the seminiferous tubes themselves, the spermatozoa are al- 

 ways inclosed in the interior of their parent vesicles; they are libe- 

 rated, and mingled promiscuously together, only after entering the 

 rete testis and the head of the epididymis. 



