Male are female sexes are separate in Ascaris and these roundworms also show sexual dimorphism. Males are smaller than the females and they also have a curved tail with pre and post anal papillae, cloaca and a pair of spicules. The gonads are long, tubular and coiled. Gonads are attached at the genital pore in females and at the cloaca in the male worms.
The male reproductive organs are confined to the posterior half of the pseudocoel.
The following are the important features of the male reproductive system,
Testis: A single testis is present in the roundworms which extend to the middle of the body. The testis is in the form of long- thread like highly twisted tube. The wall of testis is made up of single layer of cuboidal cells covered by basement membrane.
The central axis of the testis is in the form of cytoplasmic rachis around which clusters of amoeboid sperms are present in various stages of development.
Vas deferens: The distal part of the testis continues as a short, thick and twisted tube called as vas deferens. This part has a lumen which replaces the central rachis of the testis.
Seminal vesicle: Seminal vesicle is a thick, wide and muscular continuation of the vas deferens. It lies in the posterior third of the pseudocoel below the intestine.
Ejaculatory duct: The terminal part of the seminal vesicle narrows down to form highly muscular ejaculatory duct. The ejaculatory duct joins to the rectum to form cloaca. This duct contains a number of prostatic glands whose secretions help in copulation.
Penial spicules: Penial spicules are located in the spicular pouch. Two spicular pouches are situated on the dorsal side of the cloaca. These are basically evaginations of the cloaca. The penial spicules are enclosed in a spicular sheath and it consists of a cytoplasmic core surrounded by thick cuticle.
These spicules can protrude out and get retracted through the cloacal aperture by special protractor and retractor muscles. The spicules help in opening female gonopore during copulation.
Female reproductive organs lie in the posterior two third of pseudocoel.
The female reproductive organs include the following,
Ovaries: Two long, twisted, thread-like ovaries are present in Ascaris. The ovary wall consists of single layer of cuboidal epithelial cells lined externally by a basement membrane. The central axis of the ovary is in the form of cytoplasmic rachis around which groups of ova are present. Lumen is absent in the ovaries.
Oviducts: A thick, wider and twisted oviduct arises from the distal end of each ovary. The wall is similar to that of the ovary. The major difference is that the cytoplasmic rachis of the ovary is replaced by lumen in the oviducts.
Uteri: Each of the oviducts continues as a much wider and thicker and untwisted tube called the uterus. The walls of both uteri are composed of tufted cells surrounded by a muscle layer with inner circular and outer oblique fibers. The uterus serves as a storage spot for the fertilized eggs which are enclosed in the shells.
Vagina: At the anterior one third of the body the two uteri combine to form a short and highly muscular tube called vagina, having an inner lining of the cuticle. Vagina opens to the outside through female gonopore or vulva.
Formation of gametes: The gametogonia are budded off from the proximal end of the gonad. These gametogonia undergo gametogenesis as they move towards the distal end of the gonad. This method of formation of germ cell is called as telogonic and it occurs commonly in most nematodes. In a telogonic gonad, the following three zones can be identified:
Germinal zone: This zone is also known as proliferation zone. This zone lies at the proximal end of the gonad. This zone is constituted by a single large terminal cell. In front of this terminal cell, a large apical cell is present. From this apical cell, gametogonia are budded.
Growth zone: Growth zone follows the germinal zone. In this growth zone, the gametogonia lie attached to the cytoplasmic rachis. Here it grows and gets differentiated into amoeboid gametocytes.
Maturation zone: Maturation zone is the distal most zone, where the gametocytes separate from the cytoplasmic rachis to undergo maturation. After maturation, gametocytes transform into gametes. The maturation zone is followed by gonoduct.
The sperms are amoeboid whereas the ova are elliptical in shape. The ova at this stage are secondary oocytes which have developed from a single maturation division.
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