THE SEXUAL ORGANS. 621 



spermatic duct or vas deferens, which at first J J- of a line in diameter 

 and convoluted, soon increases to a size of |-1 line, and becomes 

 straight (Fig. 257, h). The epididymis, moreover, has an extremely 

 delicate fibrous tunic (J of a line) of a grayish-white color. 



198. Structure of the seminiferous tubes. The seminal tubes of 

 the testis are, in proportion to their diameter, rather more firmly con- 

 structed than other glandular canals and consist of a fibrous membrane 

 and an epithelium. The former, from 0-0024-0-005, or in the mean 

 0-003-0-004 of a line thick, composed of an indistinctly fibrous connec- 

 tive tissue with longitudinal nuclei, without muscular fibres and rarely 

 presenting an indication of elastic fibrils, is tolerably firm and exten- 

 sible. A simple layer of roundish, polygonal Fi 258 

 cells, of 0-005-0-008 of a line, occasionally 

 with an indication of a membrana propria as 

 a substratum, on the inner surface of this 

 fibrous membrane, completes the vascular ca- 

 nal, which thus obtains a wall, 0-007-0-01 of a 

 line in entire thickness. In younger subjects, 

 these cells are pale and finely granular, but 

 as age advances, a continually increasing num- 

 ber of fatty granules is collected in them, 

 whence the seminiferous tubes sometimes ac- 

 quire a light yellowish, partially brownish 

 color, which is manifest very frequently in men even at the middle 

 period of life, and invariably in old age. The ductuli recti present the 

 same structure as the tubes ; whilst in the rete testi*, no special fibrous 

 tunic can be distinguished, the canals in this portion of the gland ap- 

 pearing to be nothing more than cavities in the dense fibrous tissue of 

 the corpus Higlimorianum, lined by an epithelium. In the coni vas- 

 culosi the fibrous coat again makes its appearance, and to it there is 

 now, also, added a layer of smooth muscles, which, in the form of trans- 

 verse and longitudinal fibres, are recognizable even in canals of \ to -J- 

 of a line in diameter. The thicker portions of the canal of the epididy- 

 mis are constructed in the same way as the vasa deferentia (vid. infra\ 

 with a cylindrical epithelium, which, moreover, commences even in the 

 head of the epididyrnis. 



The contents of the seminiferous tubes vary according to age. In 

 Boys and young Animals the slender tubuli contain nothing but minute, 

 clear cells, the most external of which might be regarded as epithelial 

 cells, although not always clearly distinguishable from the others. At 

 the age of puberty, together with the increased size of the tubuli semini- 



FiG. 258. Portion of a spermatic tube in Man, magnified 350 diameters: a, fibrous coat 

 with longitudinal nuclei- 6, clear border, probably a membrana propria ; c, epithelium. 



