Paired organ on the outside is covered with tunica albuginea, formed by dense connective tissue and mesothelium of the visceral sheet of the peritoneum.

Testicular parenchyma is represented by transverse #1, #2 or tangential #1, #2 slide sections of convoluted seminiferous tubules; the main part of their wall towards the lumen is epitheliospermatogenic layer #1, #2.

The wall of the convoluted seminiferous tubule:

• is externally limited by tunica propria, including an inner layer of myoid cells #1, #2 (located on the basement membrane and have flattened fusiform nuclei) and the outer fibrous part (contains fibroblasts #1, #2);
• epitheliospermatogenic layer includes two cell pools: spermatogenic (at various stages of differentiation) and supportive (sustentocytes);
• sustentocytes #1, #2 — irregularly shaped cells lying on the basement membrane; their irregularly shaped light nuclei contain finely-dispersed chromatin and large nucleoli;
• spermatogenesis proceeds in convoluted tubules in several physically isolated steps — morphological patterns corresponding to the predominance of one or other phase of the process can be found in various parts of the tubule wall;
• main types of spermatogenic cells:
  • spermatogoniae #1, #2 — located on the basement membrane, they are isolated by hyperchromic nuclei (reproduction phase);
  • spermatocytes 1st type #1, #2 — located above the spermatogonia, containing large nuclei with a well-defined chromatin pattern (growth phase);
  • in the maturation phase spermatocytes 1st type pass sequentially the first and second meiotic divisions (lead to the formation of haploid spermatids);
  • early spermatids — small rounded haploid cells with a light nucleus in the middle;
  • late spermatids — small cells with a dense elongated nucleus in the inner layer, without flagella — at the initial and with flagella — at the late stages of spermiogenesis;
  • sperm cells are similar in structure to late spermatids, but are located in the lumen of the tubule.

Between the tubules, there is some interstitium — layers of loose fibrous connective tissue in the space between the tubules containing arterioles, venules, capillaries #1, #2 and interstitial endocrinocytes (Leydig cells) #1, #2 — large cells of rounded or polygonal shape with acidophilic cytoplasm.