CONNECTIVE TISSUE OF THE TESTIS. 275 



branes, such as surround the convoluted tubules, but is imbedded in a 

 mass of connective tissue known as the mediastinum testis (Fig. 311). 

 From the mediastinum, layers of tissue, the septula testis, extend radially 

 toward the periphery of the testis, dividing the convoluted tubules into 

 pyramidal lobules with apices toward the rete. The periphery of the 

 testis is covered with a dense connective tissue layer, the tunica albuginea. 

 It contains numerous elastic fibers which increase with age. The vis- 

 ceral layer of the tunica vaginalis rests upon its outer surface. The inner 

 portion of the albuginea is very vascular, forming a distinct layer at birth 

 (the tunica vasculosa) . Connective tissue extends from the septula among 

 the convoluted tubules. Immediately surrounding them there is a delicate 

 basement membrane followed by a layer of closely interwoven elastic 

 fibers, and flat cells. In the looser connective tissue between the tubules 



Interstitial cells. 



Connective tissue. 





FIG. 312. FROM A CROSS SECTION OP THE TESTIS OF A MAN TWENTY-TWO YEARS OLD. X 50. 



there are clumps of interstitial cells, shown in Figs. 312 and 309. They 

 are said to arise from mesenchymal cells of the genital ridge. Some- 

 times they retain protoplasmic processes, but more often they are rounded 

 or polygonal structures in close contact and without distinct cell bound- 

 aries. In their abundant protoplasm there are pigment and other gran- 

 ules, fat droplets, and rod shaped crystalloids. (Rod and spindle shaped 

 crystalloids are also found in the spermatogonia at all ages, and after 

 puberty octahedral forms occur. Rod shaped forms in the sustentacular 

 cells have already been mentioned. The composition and significance 

 of all these are unknown, but they are not considered post mortem for- 

 mations.) 



The interstitial cells, although not intimately related with the vessels, 

 are thought to produce an internal secretion, and there is evidence that 

 upon it the sexual instinct depends. During senile atrophy of the testis 



