The excretory system is composed of a pair of kidneys, ureters, cloaca and urinary bladder. The kidneys are compact, dark red and bean-like structures. The kidneys are situated a little posteriorly in the body cavity; on both sides of the vertebral column.
Each kidney is composed of several nephrons. Two ureters emerge from the kidneys in the male frogs. In males, the ureters act as urogenital duct and opens into the cloaca. In females, the ureters and oviduct open separately in the cloaca. The frog is a ureotelic animal.
Control & Coordination
Frog has a highly evolved neural system and endocrine glands.
Coordination By Hormones
Hormones are secreted by various endocrine glands and facilitate chemical coordination. The main endocrine glands in frog are; pituitary, thyroid, parathyroid, thymus, pineal body, pancreatic islets, adrenal and gonads.
The nervous system is organized into central nervous system, peripheral nervous system and autonomic nervous system.
Central Nervous System: The central nervous system is composed of the brain and the nerve cord. The brain is enclosed in a bony structure; called brain box or cranium. The brain is divided into forebrain, midbrain and hindbrain.
- Forebrain includes olfactory lobes, paired cerebral hemispheres and unpaired diencephalon.
- A pair of optic lobes is present in the midbrain.
- The hindbrain consists of cerebellum and medulla oblongata. The medulla passes out through the foramen magnum and continues into the spinal cord. The spinal cord is enclosed in the vertebral column.
- Ten pairs of cranial nerves arise from the brain.
Sense Organs: Organs of touch (sensory papillae), taste buds, olfactory receptors (in nasal epithelium), eyes and internal ears are the sense organs of frog. The eyes and internal ears are well developed, but the rest of the sense organs are cellular aggregations around nerve endings.
Frogs have simple eyes. The ear also serves as the organ of balancing (equilibrium).
Male Reproductive Organs
The male reproductive system of frog is composed of a pair of yellowish ovoid testes. The testes are adhered to the upper part of kidneys by a double fold of peritoneum called merorchium. There 10 – 12 vasa efferentia arising from the testes. They enter the kidneys on their side and open into Bidder’s canal. Finally, it communicates with the urinogenital duct which comes out of the kidneys. The urogenital ducts open into the cloaca. The cloaca is used to pass faecal matter, urine and sperms to the exterior.
Female Reproductive Organs
There is a pair of ovaries which are situated near kidneys. There is no functional connection between the ovaries and the kidneys. The oviducts open separately into the cloaca. A female frog can lay 2500 to 3000 ova at a time.
Fertilisation is external and takes place in water. Development is indirect and the larva is called tadpole.
Significance of Frogs for Humans
Frogs eat insects and thus protect the crops. Frogs serve as an important link in the food chain and hence maintain the ecosystem. Frog meat is used as delicacy in some countries.