

THE SEXUAL ORGANS. 225 



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 transverse and longitudinal fibres, are recognisable 

 even in canals of \ to ^" in diameter. The thicker portions of 

 the canal of the epididymis 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 epididymis. 

 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 seminiferi, the 

 elements contained in them also increase in circumference ; and 

 when the formation of semen has actually commenced, they 

 appear as clear, round cells and cysts of 0*005 — O'OS'", which, 

 according to their size, enclose a variable number of, from 1 to 

 10, or even 20, clear nuclei of 0-0025 — 0-0035'" with nucleoli. 

 At this time, in many cases, an epithelium is not manifest, the 

 seminal tubes rather appearing to be occupied entirely and 

 solely by the cells in question ; at other F j g< 259. 



times, and particularly in advanced years, 

 an epithelium is presented containing fat- 

 or pigment-cells, and surrounding the other 

 elements. The latter, whether they occur 

 in the one way or the other, are the pre- 

 cursors of the semen, which, in the mature 

 condition, entirely consists of an extremely 

 small quantity of a viscid fluid, and of innu- 

 merable minute, linear corpuscles having 

 a peculiar movement, the spermatic fila- 

 ments or animalcules, fila spermatica, sper- 

 matozoa (also spermatozoida). These sper- 

 matic filaments are perfectly homogeneous, soft corpuscles, 

 in which are distinguishable a thicker portion — the body or 

 head, — and a filamentary appendage, — the filament or tail. The 

 former is flattened and, viewed on the side, pyriform, with the 

 acute end in front; on the surface oval, or even rounded ante- 

 Fig. 259. Spermatic filaments (human); 1, x 350 diam.; 2, x 800 diam.: a, 

 viewed on the edge ; b, on the flat surface. 



11. 15 



