Anatomical and histological studies on the male reproductive system of the red swamp crayfish Procambarus clarkii.

The male reproductive system of Procambarus clarkii consists of two milky white testes; each one consists of anterior and posterior portions. The two testes are separated anteriorly and united posteriorly. A collecting duct arisesfrom each testis. These ducts meet together at the middle point between the anterior and posterior testes, from this point; a long coiled, thread-like vas deferens extends. It is tubular and white in colour. The right one is longer,thicker and coiled, while the left one is shorter transparent and not coiled. Both the left and right vasa deferentia extend posteriorely to open with the male gonopore on the last thoracic appendages. Histologically, the testis consists ofacini in which stages of spermatogenesis occur. Spermatides pass to the collecting tubules, where they become mature sperm and packed in a spermatophore in the vas deferens. The wall of the collecting tubules consists ofsimple cuboidal cells. The vas deferens is divided into two regions; the glandular and ejaculatory regions. The first is lined with secretory columnar epithelium, while the second has a muscular wall of longitudinal and circular muscles andlined with single layer of ciliated columnar epithelium.