XXXV.] THE TESTIS. 383 



the tubes are lined by several layers of more or less cubical cells, 

 whose nuclei stain more or less deeply with staining reagents. In 

 an active gland in some tubules some of the clear cubical cells of 

 the outer row of cells lining epithelium contain nuclei under- 

 going mitotic division. The rows of cubical cells internal to these 

 have a radiate arrangement, and are separated into groups by larger 

 structures, sometimes called spermatoblasts, and by other observers 

 sustentacular cells, which grow up between the smaller cells, 

 and at their upper ends are connected with the spermatozoa. Inside 

 the layer of lining epithelial cells are several rows of larger cells 

 spermatogenic cells with nuclei showing different stages of 

 mitosis. Next the lumen, which is always well defined, in some of 

 the tubules are spermatozoa in different stages of development. In 

 others, however, not so far advanced, the inner row of cells consists 

 of small protoplasmic cells the true spermatoblasts as from these 

 cells the spermatozoa are developed. The developing spermatozoa 

 rest by means of their heads on the sustentacular cells. The sper- 

 matozoa are arranged in tufts or groups, with their tails towards 

 the lumen. The spermatozoa gradually develop from the true 

 spermatoblasts and pass towards the lumen, and as they are set 

 free new spermatoblasts are formed by the mitotic division of the 

 spermatogenic cells. 



The straight tubules are lined by a single layer of flattened 

 epithelium ; the rete testis has no basement membrane, but it 

 also is lined by a single layer of flattened epithelium. The vasa 

 efferentia and the tube of the epididymis have smooth muscular 

 fibres in their walls, and are lined by columnar ciliated epithelium, 

 the cilia being very long. 



The interstitial tissue of the testis between the tubules is very 

 loose in texture and laminated, and has numerous lymphatic slits. 

 In some animals (rat, boar) are numerous polyhedral, nucleated, 

 sometimes pigmented, cells, the remains of the cells of the Wolman 

 bodies. 



The vas deferens consists of a fibrous coat investing an outer 

 thick layer of smooth muscle arranged longitudinally ; inside this 

 is a thick layer of smooth muscle arranged circularly ; inside this 

 again is a submucous coat of connective tissue. In some parts of the 

 tube there is a layer of smooth muscle arranged longitudinally just 

 internal to the circular coat. Then follows the mucosa lined by 

 columnar non-ciliated epithelium. 



Methods. (i.) Harden the fresh testis in M tiller's fluid (2 

 weeks). If it be large, cut it into small pieces. The capsule exerts 

 considerable pressure on the gland substance, so that when the testis 

 is cut into, the latter projects somewhat. Complete the hardening 

 in alcohol. Corrosive sublimate is a good hardening reagent. Stain 



