Reproductive System of Frog

Reproductive System

• Unisexual with sexual dimorphism. Male has vocal sacs and nuptial pads.
• Testes are oval, yellowish connected to the kidney and also to the inner surface of dorsal body wall by mesorchium.
• Testes are made up of seminiferous tubules for producing sperms. From each testis 10-15 small ducts come out and are linked to Bidder’s canal present at the inner margin of the kidney. Bidder’s canal transports sperms to ureter via collecting tubules.
• In some species of frog, in breeding season, the distal part of the urinogenital duct dilates to form a temporary seminal vesicle. Sperms are stored temporarily in the seminal vesicle before copulation. (No seminal vesicle is present in Rana tigrina). Male cloaca is known as urinogenital sinus as it receives urine as well as sperms. The copulatory organs are absent.
• Mass of sperms released out by male during copulation is called milt.
• Female reproductive system has a pair of an irregularly lobed, large ovary attached to the antero-ventral part of each kidney and also inner surface of dorsal body wall called mesovarium.

Fig. Reproductive system of a female frog (ventral view)

• Ovary contains a number of follicles with various development stages of ova. Mature ova breaks through the follicle, ovarian wall and released into the body cavity (ovulation).
• The ovum of the frog is telolecithal. The side having yolk is called vegetal pole and the opposite end is animal pole. Paired long, convoluted, whitish tube are present on either side of the
• body cavity and open into body cavity through ciliated funnel-like openings called ostia at the level of oesophagus.
• An enlargement (ovisac) is present with each oviduct before opening into cloaca for temporary storage of ova.
• Mass of ova released by female frog during copulation is called spawning. When laid, the eggs are enclosed in jelly which is mainly protective.
• Fertilization external. Each egg undergoes cleavage, blastula stage, gastrula stage followed by development of larva called tadpole larva inside the egg.
• Larva swims actively in water with the help of tail and its caudal fin. It has three pairs of external gills for respiration. It is herbivorous with a long and coiled intestine.
• With further growth, develops four pairs of gill-slits in the region of pharynx and operculum opens out through a branchial aperture on left side.
• Forelimb buds are covered by opercula. It respires with gill for sometime and lungs for sometime.
• During metamorphosis, tail starts disappearing, gills disappear, pronephric kidney changes to mesonephric, hind limb grow longer, lateral line organ disappear. Thyroxine is required for metamorphsis.
• Maximum changes during metamorphosis occur in blood vascular system while minimum changes take places in nervous system.

Common names of other frogs/toads

Bufo : Indian toad

Alytes : Midwife toad

Hyla : Tree frog

Rhacophorus : Flying frog

Gastrotheca : Marsupial frog

Bombinator : Fire-bellied toad

Pipa : Surinam toad