Brief note on the reproductive system in Amphibia

In amphibian, the sexes are separate and the reproductive system can be studied as:

A. Male reproductive system

B. Female reproductive system

A. Male reproductive System:

The male reproductive system consists of:

1) A pair of testes.

a) Vasa efferentia

b) Bidder’s canal

c) Collecting Table Associated ducts.

d) Urinogentital duct

e) Cloaca

A pair of testes: There is a pair of dark yellow color, oval or cylindrical testes found closely attached to kidney.

Microscopic Structure:

Each testis consists of numerous coiled tubes called somniferous tubes and these tubes remain associated with interstitial cells. Interstitial cells secrete a hormone called testosterone which is responsible for development of secondary sexual characters.

Somniferous Tabules:

Each somniferous tubule is circular or oval lined with germinal epithelium. These germinal epithelial cells undergo the process of spermatogenesis to produce spermatozoa (the male sex cells).

Associated ducts: From each testis, arise about 10 to 12 fine ducts called vasa-efferentia.

Vase-efferentia open into the Bidder’s canal and the Bidder’s canal is connected to longitudinal collecting tubules by means of a number of transverse collecting ducts. The longitudinal collecting tubules open into the ureter.

In male both urine and sperms pass through a common duct called urinogenital duct. The urinogenital duct is expanded to form seminal vesicle. Seminal vesicle stores the sperms until they are sent out at the time of copulation.

So the spermatic fluid containing sperms are produced inside the testis and passes successfully through vasa-efferentia, Bidder’s canal, transverse collecting duct. Urinogenital duct and finally stored in the seminal vesicle. During copulation, sperms are ejected outside through the cloaca.

Female Reproductive System:

Female reproductive system of amphibian consists of 1. A pair of ovary, 2. Oviducts, 3. Ovisacs (Uterus), 4. Cloaca.

Ovaries:

The ovaries are a pair of loose lobulated and thin walled sac, attached to the kidney an the ventral surface by a fold of peritoneum called mesovarium. Ovaries are yellow colored and irregular in shape, but during breeding season they become much enlarged and extended into the body cavity assuming black coloration. On the surface of ovary there are many rounded projections which passes ova or eggs in various stages of development.

Microscopic structure of the ovary:

The ovary is lined with an outer layer of peritoneal epithelium and inner layer of germinal epithelium comprising single layer of germinal cells. in between the two layers lies connective tissue, nerve fibers and blood vessels.

The germinal cells undergo the process of Oogenesis to form mature ova. The mature ovum is large size due to the accumulation of yolk materials. It contains single nucleus and more nucleoli. The ovum is surrounded by inner vitelline membrane and outer follicular epithelium.

The cells of germinal epithelium undergo rapid division and form many small groups of cells, called ovarian follicle. But one of the cell of the ovarian follicle becomes larger grows in size and become the ovum. But the remaining cells surround the ovum in single layer to form follicular epithelium which provides nourishment to the ovum, within the follicle; the ovum secretes a vitelline membrane around itself. The ova ore enlarged during breeding season by the growth of the cytoplasm.

Oviduct:

The paired oviducts are long, coild, whitish tube extend anteriorly up to the base of the lungs on either side and open into the coelomic, through cup shaped ostia. The opening of ostia is lined with cilia, which beat constantly in order to the anterior part of the oviduct, which is thin and narrow. The middle part of the oviduct is longest, much coiled, thick walled and lined internally with glandular epithelium which secrets an albuminous fluid.

Ovisac:

The posterior most part of the oviduct is dilated to form a brand, thin walled and highly distensible sac, called ovisac or uterus. The ovisac serves for the storage of ova until copulations. The two ovisacs open separately in the dorsal wall of the cloaca and opposite to the opening of the urinary bladder.

When ova become fully mature, the peritoneal covering of ovary bursts releasing the ova into the coelomic fluid of the body cavity where they float. This is called ovulation. The ova are drawn into ostia and pass in to the lumen of oviducts. Finally, they reach the ovisac where they remain for temporary period. During copulation, the ova gradually come into the cloaca and pass out through the cloacae aperture. When the eggs come in contact with water, the albuminous fluid around them becomes jelly like and form a frothy mass called spawn. Because it has got the property to absorb water for which there is enormous swelling of the eggs to form spawn.