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The development of frog is divided into two phases: 1. Pre-natal or Embryonic development ·   It is the development that takes place inside the egg or inside the womb of the mother up to the gastrula stage from the zygote. 2. Post-natal or Organogenesis ·   In this period, development from the birth of an organism to death is studied or the formation of organs from three germinal layers. a. Breeding: ·  Breeding takes place during the rainy season, in water. ·  Male frog croaks (mating call) by staying at shallow water region at night time to attract females.  ·   Many female frogs attract towards a male frog and male frog mounts over a female frog. ·  This Sexual embracing condition is called  amplexus or pseudocopulation . ·   Then the females lay the eggs in water and the male also releases the sperms. b. Ovulation: ·  It is a process of release of secondary oocytes from the ovary to the body cavity. c. Spawning: ·  When the...

· Frog is  unisexual. · Well-marked sexual dimorphism  is seen. ·   Males can be differentiated from females by: More muscular upper limbs. Vocal sacs at the ventral surface of the head. Nuptial pads at the base of the index finger of the forelimb. · Fertilization is external. ·   Larval stage is present during the development. Male Reproductive Organs 1. Testes · Paired, oval bodies lying ventral to kidneys to which they are suspended by a double fold of peritoneum called  mesorchium . · Histologically,  testis consists of a large number of  Seminiferous  tubules → lined by germinal epithelium that gives rise to sperms (spermatogenesis). · Between the tubules: Interstitial cells or Leydig's cells → secret Testosterone which maintains secondary sexual characters. · Fat bodies are attached to the anterior end which is used in hibernation and aestivation for the energy of a frog. 2. Vasa Efferentia ·   Arise from testes 10-12 in number on...

Lymphatic System · Lymph is formed by extravasation or filtration of blood from the arteriolar end of capillaries into the tissue spaces. · Similar in composition to plasma except for the absence of large molecular weight proteins. · Lympth or tissue fluid → lymph capillaries → lymph sinuses → lymph hearts → veins · Lacks RBCs and thrombocytes. · Lymph helps in absorption of fat in the small intestine. · The lymphatic system consists of lymphatics or lymph vessels- thin wall delicate vessels of different sizes. · Larger vessels open into the venous system ·  Lymph heart:  small rhythmically contractile in nature. The frog has 2 pairs of lymph hearts: · One pair is located  anteriorly  below scapulae and opens into the  subscapular  vein. · Other pair located on either side of  urostyle  and open into femoral veins. ·  Lymph spaces:  about 20 subcutaneous lymph sinuses under the skin (example: dorsal, lateral...

· Generally veins collect blood from different parts of the body to the heart. · However, there are some veins that before reaching the heart carry blood to some other organs where they form a network of capillaries. · These are portal veins. · Organs that receive blood from portal veins are called portal organs. · Examples: liver, kidneys etc. · So, the portal system is a system of veins carrying blood from one organ to another instead of carrying it to the heart. · There are two portal systems in the frog. · They are the hepatic portal system and renal portal system. A. HEPATIC PORTAL SYSTEM · It consists of veins collecting blood from different parts of the alimentary canal and hind limbs to the liver. · It consists of the following veins. (a) Anterior Abdominal Vein: · It is formed by the union of two pelvic veins and vesicular veins. · Pelvic veins are the lateral branches of the femoral veins from the hind limbs which collect blood from the outer parts of the hind limbs. · Th...

·  This system consists of blood vascular and lymphatic systems. ·   It is the closed type and represents single circulation due to the mixing of both pure and impure blood. A. Blood Vascular System ·  It includes the heart and blood vessels. a. Blood · Fluid connective tissue · Mesodermal in origin · Consists of blood plasma and blood corpuscles. i. Blood plasma · Colorless or faint yellowish fluid. · Forms 2/3rd of blood volume. · Consists of: 1. Water 2. Inorganic substances (Na+, K+, Cl–, HCO3–) 3. Acids, glucose, hormones, absorbed food materials, excretory products, antibodies etc. · Blood corpuscles are of three types: RBCs, WBCs and Platelets. 1. RBC or ERYTHROCYTES · Flattened, more or less elliptical. Biconvex when viewed along its edge. · 22μ ✕ 16μ in dimension,  · The average age of RBCin frog is  100 days. (RBC life span in humans is 120 Days or 4 months.) · 3000-4000/mm3 · Nucleated · Produced in kidneys, liver and spleen. · The bones of fro...