1. Phylum
    2. 1. Classification of Animals
    2. Protozoa
    3. Porifera
    4. Coelenterata
    5. Platyhelminthes
    6. Nemathelminthes
    7. Annelida
    8. Earthworm
    9. Arthropoda
    10. Cockroach
    11. Mosquito
    12. Honey bee and Silk moth
    13. Mollusca
    14. Echinodermata
    15. Hemichordata
    16. Chordata
    17. Pisces
    18. Amphibia
    19. Frog
    20. Reptile
    21. Aves
    22. Mammalia
    23. Rabbit bone
  2. Animal Behaviour and Adaptation
    3. 24. Animal behaviour
    25. Animal adaptation
    26. Migration
  3. Developmental Biology
    4. 27. Development of Animals
    28. Development of Frog
  4. Human Biology
    5. 29. Tissues
    30. Sense organs
    31. Digestive system
    32. Circulatory system
    33. Respiratory system
    34. Nervous system
    35. Endocrine system
    36. Reproductive system
    37. Excretory system
    38. Skeletal system
    39. Basic concept of Immunology
    40. Human diseases
  5. Evolutionary Biology
    6. 41. Origin of Life
    42. Organic Evolution
    43. Theories of Evolution
    44. Evolution of Human beings
    45. Horse Evolution
Developmental Biology
28. Development of Frog
▢ Breeding:
  1. Frog breeds in the rainy season, June to September.
  2. Frog breeds like other amphibians in water.
  3. Male frogs produce croaking sound (mating call) by their vocal sacs.
  4. The sexual embrace of the male and female frogs is called amplexus (false copulation).
  5. The purpose of amplexus is to ensure simultaneous discharge of male and female gametes at the same place in water.
▢ Ovulation:
  1. Ovulation is the release of eggs from ovary into the body cavity.
  2. The eggs in the stage of secondary oocytes are released into the body cavity by rupture of ovary.
▢ Spawning:
  1. Spawning is the act of laying of eggs by the female frog, stimulated by the male during amplexus.
  2. Spawn is a cluster or mass of eggs laid by a female.
    3. ◉ Egg structure:
    1. The egg is surrounded by a thin vitelline membrane and three layers of jelly coats made of gelatin.
    2. Gelatin protects the egg from predators and acts as an insulator keeping the egg warm.
▢ Structure of Egg:
  1. Frog’s egg is mesolecithal (based on amount of yolk) and telolecithal (based on distribution).
  2. Upper pigmented part is animal hemisphere; lower unpigmented part is vegetal hemisphere.
  3. Cytoplasm is concentrated in animal pole.
  4. Vegetal hemisphere contains yolk and remains directed downwards.
    5. ◉ Developmental sequence:
    1. Fertilization
    2. Cleavage
    3. Morula
    4. Blastula
    5. Gastrula
▢ Fertilization:
  1. Fertilization in frog is external and occurs in water.
  2. Sperms are released on the egg mass before it reaches water.
  3. Second meiotic division occurs when sperm enters the egg.
  4. Sperm enters at the animal hemisphere.
    5. ◉ Grey Crescent:
    1. Appears in equatorial zone opposite to sperm entry.
    2. Marks the dorsal side of the future embryo.
    ◉ Sperm Entry Point:
    1. Marks anterior side of future embryo.
    2. Establishes bilateral organization.
    3. The entry point region is called 'reception cone'.
▢ Cleavage:
❖ Definition: Early mitotic divisions of zygote up to blastula stage; cleavage is indeterminate (regulative development).
❖ Stages:
◉ 1st Cleavage:
  1. Meridional, holoblastic, and equal.
  2. Furrow appears at animal pole forming two blastomeres (right and left).
◉ 2nd Cleavage:
  1. Holoblastic and equal.
  2. Forms 4 cells; grey crescent present only in two dorsal blastomeres.
◉ 3rd Cleavage:
  1. Holoblastic and unequal.
  2. Plane is horizontal, above equator (latitudinal).
    3. ■ Blastomeres:
    ● Upper four:
    1. Smaller (micromeres)
    2. Pigmented
    3. No yolk
    ● Lower four:
    1. Larger (macromeres)
    2. Non-pigmented
    3. Yolk-laden
◉ 4th Cleavage: Two synchronous meridional divisions; forms 16 blastomeres.
◉ 5th Cleavage: Two simultaneous latitudinal divisions; forms 32 blastomeres.
◉ 6th Cleavage: Divisions become irregular and asynchronous; micromeres divide faster than macromeres.
◉ 7th Cleavage: Embryo appears as a morula (mulberry-shaped ball of cells).
◉ Morula: Solid ball of cells.
◉ Blastula:
  1. Cavity (blastocoel) appears toward animal hemisphere; frog blastula is Coeloblastula.
  2. Blastocoel contains albuminous fluid secreted by surrounding cells.
▢ Gastrula:
❖ Definition: Conversion of blastula into three-layered gastrula with archenteron.
❖ Germ layers:
  1. Ectoderm
  2. Mesoderm
  3. Endoderm
❖ Movements:
◉ Epiboly: Migration and spreading of micromeres over the embryo.
◉ Invagination:
  1. Occurs below equator below grey crescent midpoint.
  2. Forms a slit leading to blastopore.
◉ Involution:
  1. Chordamesoderm cells insink and move anteriorly along blastocoel roof.
  2. Failure of involution halts development (no gastrulation).
❖ Cavities:
◉ Archenteron: Future gut cavity.
◉ Blastopore:
  1. Opens into archenteron.
  2. Gives rise to anus in frog.
❖ Other processes:
  1. Ingression: Migration of individual vegetal cells to embryo interior.
  2. Blastocoel reduces by end of gastrulation; yolk plug (endodermal) closes blastopore.
  3. Yolk plug side represents posterior side of future tadpole.
▢ Neurula:
❖ Neurulation: Occurs after gastrulation; neural tube is formed.
❖ Formations:
  1. Neural tube
  2. Notochord (Notogenesis)
  3. Gut
▢ Metamorphosis:
❖ Hormone: Thyroxin secreted by thyroid gland initiates metamorphosis.
❖ Influencing factors:
  1. Delayed by food abundance.
  2. Favoured by food deficiency.
❖ Tadpole nature: Herbivorous.
❖ Changes:
  1. Feeding stops; tail stores provide nutrition.
  2. Tail shortens.
  3. Larval epidermis and horny jaws are lost.
  4. Glands develop in skin.
  5. Lungs become functional; gill clefts close.
  6. Blood vascular system modified.
  7. True jaws formed.
  8. Eyes move to top and bulge.
  9. Tongue enlarges, intestine shortens, stomach and liver enlarge.
  10. Forelimbs develop; young frog leaves water.
  11. Feeds, grows, and loses remaining tail.