778 EiMBRYOLOGY 



(7.6 decimeters), and its diameter is ^-J-^ to T | T of an inch (125 to 166 ^). 

 It begins by two to seven short blind extremities and sometimes by 

 anastomosing loops. The caecal diverticula usually are found in the 

 external half of the tube, and their length is ^ to | of an inch (2.1 to 

 3.2 millimeters). The anastomoses are sometimes between the tubes of 

 different lobules, sometimes between tubes in the same lobule and some- 

 times between different points in the same tube. As the tubes pass 

 toward the posterior part of the testicle, they unite into twenty to thirty 

 straight canals, called the vasa recta, about -^ of an inch (0.5 milli- 

 meter) in diameter, which penetrate the mediastinum testis. In the 

 mediastinum the tubes form a close network, called the rete testis ; and 

 at the upper part of the posterior border they pass out of the testicle, 

 by twelve to fifteen or twenty ducts, called vasa efferentia. 



Having passed out of the testicle, the vasa efferentia form a series 

 of small conical masses, which together constitute the globus major, or 

 head of the epididymis. Each of these tubes when unravelled is six to 

 eight inches (15 to 20 centimeters) long, gradually increasing in diameter, 

 until they all unite into a single convoluted tube, which forms the body 

 and the globus minor of the epididymis. This single tube of the 

 epididymis, when unravelled, is about twenty feet (6 meters) in length. 



The walls of the seminiferous tubes in the testicle itself are com- 

 posed of connective tissue and of peculiar structures that will be fully 

 described in connection with spermatogenesis. In the rete testis it is 

 uncertain whether the tubes have a special fibrous coat or are simple 

 channels in the fibrous structure. They are here lined with squamous 

 epithelium. . In the vasa efferentia and the epididymis, there is a fibrous 

 membrane, with longitudinal and circular fibres of non-striated muscular 

 tissue and a lining of ciliated epithelium. The movements of the cilia 

 are toward the vas deferens. In the lower portion of the epididymis the 

 cilia are absent. The tubular structures of the testicle, the epididymis 

 and the beginning of the vas deferens are shown in Fig. 210. 



At the lower part of the epididymis, communicating with the canal, 

 there usually is found a small mass, formed of a convoluted tube of 

 variable length, called the vas aberrans of Haller (5, A, A, Fig. 210). 

 This sometimes is wanting. 



Interstitial Gland of the Testis. Lying between the seminiferous 

 tubes and apparently giving support to them, are collections of delicate 

 fibres of areolar tissue with abundant bloodvessels, large cytoplasmic 

 cells and sometimes fatty and pigmentary globules and granules. These 

 structures are said by some anatomists to constitute an interstitial gland 

 that influences the development of spermatozoids and may be the seat of 

 an " internal secretion." 



