558 MANUAL OF HISTOLOGY. 



The interior of these tubes is filled with cells, of which the most peri- 

 pheral may cover the membrana propria in a manner similar to epithe- 

 lium. They are usually roundish or polygonal, and from '01 13-0 '01 42 

 mm. in transverse section. They are composed in young subjects of a 

 finely granular, rather pale substance (containing yellow pigment in man), 

 which becomes charged in the course of years with an ever-increasing 

 number of fatty granules. These cells of the testes have been observed 

 even in embryos to be endowed with contractility, and to possess the power 

 of amoeboid change of form (La Vedette St George). 



Recently, however, a more complex structure has been ascribed to the 

 seminal tubes. 



In man and the ox, for instance, a framework of flat stellate cells with 

 membraneous processes is stated to exist in their interior (Sertoli, M&rkd, 

 Boll). We regarded these, the " sustentacular cells " of Merkel. as the 

 same network to which we have already had such frequent occasion to 

 allude in dealing with the racemose glands. Milialkowicz, on the 

 other hand, in his excellent work, declares this appearance of sustentacular 

 cells to be an artificial production caused by the coagulation of an albumi- 

 nous material between the seminal cells. 



Such is the structure of the seminiferous tubes as far as the rete testis, 

 in which for the time being their external fibrous tunic is fused into the 

 connective-tissue of the corpus Highmori. The tubes, which leave the 

 latter as they increase in size, obtain an additional layer of smooth muscular 

 fibres, which is further strengthened lower down in the body of the epidi- 

 dymis by two coats of longitudinal fibres, an external and an internal. 

 This arrangement we shall again meet with in the vas deferens. 



We have already (p. 150) alluded to the peculiar ciliated epithelium of 

 the epididymis. 



The blood-vessels of the testes are branches of the internal spermatic 

 artery. They penetrate into the interior of the organ-form without, and 

 from the corpus Highmori, and take their further course along the septa 

 dividing as they go. Finally, they break up into a long-meshed, rather 

 loose capillary network of somewhat contorted vessels, from '0128 to 

 0-0056 mm. in diameter (fig. 546, 1, c; 547, c), which invests the semini- 

 ferous tubes. The vascularity of the epididymis, which is supplied by 

 the arteria vasis deferentis Cooj)eri, is no less considerable. The veins 

 present the same arrangement as the arteries. 



The lymphatics of the parenchyma of the organ, lined by the special 

 cells of such vessels (Tommasi), occupy the soft interstitial connective- 

 tissue of the former, arranged in a close network of canals (fig. 546 1, c; 

 547, d). In transverse sections of the seminiferous tubes, it may be seen 

 that these lymphatic canals form regular rings around the latter, of pas- 

 sages from 0'0128 to 0'0292 mm. in diameter, and strongly dilated at the 

 points of junction with each other. Steady injection at last drives the 

 fluid employed through the external cellular layers of the Avails of the 

 seminiferous tubes. The most internal layer alone is entirely impervious 

 (Mihalkowicz). The blood-vessels, also, are here and there ensheathed 

 in lymph streams. 



From the rings just mentioned other lymphatic canals are given off to 

 the numerous connective-tissue septa of the lobules. Under the albuginea, 

 also, they are arranged in a very complex network of wide canals, and 

 then penetrate the former in the form of wide-valved intercommunicating 

 passages, most highly developed on the dorsum of the organ. Finally, 



