STRUCTURE OF THE TESTICLE. 447 



interior of the gland. This vascular network, together with its con- 

 necting areolar tissue, constitutes the tunica vasculosa of Astley Cooper. 



Minute structure. — Seminal tubes. — The proper glandular sub- 

 stance of the testicle is a soft but consistent mass of a reddish-yellow 

 colour, which is divided into numerous small lobes of conical form, with 

 the larger ends turned towards the surface of the testicle, and the smaller 

 towards the mediastinum. The number of these lolics (lobuli testis) 

 has been estimated at 250 by Berres, and at upwards of 400 by 

 Krause. They differ m size according to their position, those which 

 occupy the middle of the gland and reach its anterior border being- 

 longer and larger than the rest. They consist almost entirely of small 

 convoluted tubes, named tuhuU seminiferi, in the interior of which 

 the seminal product is secreted. Each lobe contains one, two, three, 

 or even more of these convoluted tubules, the coils of which, 

 being only loosely held together, may be more or less successfully 

 unravelled by careful dissection under water. Lauth estimates their 

 mean number to be 840, and the average length of each two feet and a 

 quarter. Their diameter, which is uniform throughout their whole 

 course, is from ^~>o^\'i to -x^-Qih. of an inch. They present two kinds of 

 convolutions, each tube having a fine and regular undulation, which 

 gives a granular appearance to the whole mass, and this undulatiug tube 

 being again thrown into complicated folds, which are compressed so 

 as to be elongated in the direction of the lobule. The lobules are 

 never quite distinct, for here and there tubules are always to be found 

 passing from one to another; and it sometimes happens that lobules 

 which are divided by a distinct plane of contact at one part, are 

 intimately connected at another ; so that the division of the mass into 

 lobules varies greatly in its extent, and hence the different estimates of 

 the number of the lobules by different anatomists. The walls of the 

 tubuli seminiferi are composed of a basement membrane consisting of 

 several layers of flattened cells (Mihalkovics). The walls of the tubes 

 are sufficiently strong to bear the forcible injection of mercury, which 

 has been commonly employed for their investigation and their display in 

 preserved specimens. 



The mode in which the tubes commence appears to be twofold — viz., 

 by free closed extremities, hid within the lobules, but more frequently 

 by anastomosing arches or loops. After an exceedingly tortuous course, 

 they at length, in approaching the corpus Highmori, become at first 

 slightly fiexuous and then nearly straight. The separate tubuli of each 

 lobe, and then those of adjoining lobes, unite together into larger 

 tubes, which enter the fibrous tissue of the mediastinum and, being 

 placed amongst the branches of the blood-vessels, form the straight 

 tubes or vasa recta. 



Spermatic Cells. — The interior of the tubes is occupied by cellular 

 contents Avhich, in the young subject, assume somewhat the appearance 

 of an epithelial lining, but in the adult fill the whole tube with a con- 

 fused mass of cells. In some instances, however, the cells are ranged 

 in radii from the circumference to the centre, and a passage or lumen 

 is left in the interior. Throughout the mass the cells are in various stages 

 of advance towards the formation of the seminal product, some fully 

 formed spermatic filaments being seen in the centre, and the cells of the 

 circumference being least developed. 



It has been asserted by some observers that the spermatic cells are 



