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
27. Development of Animals
▢ Implantation:
❖ Timing: After 32-celled stage
▢ Introduction:
❖ Definition: The study of development of an organism is called ‘Embryology’ or ‘Developmental biology’
❖ Scope: Deals with developmental changes from zygote to death
❖ Key Terms:
◉ Embryogenesis/Ontogenesis: Entire process of development
◉ Blastogenesis: Development from asexual reproductive body
◉ Embryogenesis (strict sense): Development from fertilized egg/zygote
❖ Historical Figures:
◉ Founder: Aristotle
◉ Father of Modern Embryology: Karl Ernst Von Baer
❖ Reproductive Types:
◉ Oviparous:
◈ Description: Egg-laying animals (external embryonic development)
◈ Examples:
  1. Insects
  2. Fishes
  3. Amphibians
  4. Reptiles
  5. Birds
◉ Ovoviviparous:
◈ Description: Egg develops inside maternal body without maternal nourishment
◉ Viviparous:
◈ Description: Embryo develops in uterine wall until birth
◈ Examples:
  1. Eutherian mammals
  2. Some elasmobranch fishes
  3. Reptiles
◉ Parthenogenesis:
◈ Description: Virgin birth (development without fertilization)
◈ Example: Lacerta saxicola (Russian lizard)
❖ Specialized Studies:
◉ Teratology: Study of abnormal embryonic development
▢ General Phases of Development:
❖ Eggs:
◉ Chalazae: Suspensory ligaments of yolk in bird's egg
◉ Classification:
◈ Based on Yolk Amount:
    ● Type: Microlecithal (Alecithal)
    ● Description: Small/negligible yolk
    ● Examples:
    1. Starfish
    2. Amphioxus
    3. Eutherian mammals
    ● Note: Human egg is alecithal
    ● Type: Mesolecithal
    ● Description: Moderate yolk
    ● Example: Amphibians (frog)
    ● Type: Macrolecithal
    ● Description: Large yolk
    ● Examples:
    1. Arthropods
    2. Fishes
    3. Reptiles
    4. Birds
    5. Prototherians
◈ Based on Yolk Distribution:
    ● Type: Isolecithal
    ● Description: Uniform yolk distribution
    ● Examples:
    1. Protochordates
    2. Echinoderms
    ● Type: Telolecithal
    ● Description: Yolk concentrated at vegetal pole
    ● Examples:
    1. Frog
    2. Reptiles
    3. Aves
    4. Fishes
    ● Type: Centrolecithal
    ● Description: Central yolk concentration
    ● Example: Arthropods
◈ Based on Shell:
    ● Type: Acleidoic
    ● Description: No shell
    ● Type: Cleidoic
    ● Description: Insulated eggs (albumen + membranes + shell)
    ● Composition: Shell: 94% calcium carbonate
◉ Egg Membranes:
    ■ Type: Primary
    ■ Formation: Secreted by ovum
    ■ Examples:
    1. Jelly envelope (Echinoderms)
    2. Vitelline membrane (Molluscs, amphibians, birds)
    3. Zona pellucida (Mammals)
    ■ Type: Secondary
    ■ Formation: By ovarian follicle cells
    ■ Example: Chorion (insects)
    ■ Type: Tertiary
    ■ Formation: By maternal genital tract
    ■ Examples:
    1. Frog: Albuminous jelly layers
    2. Birds/Reptiles: Albumen + shell
❖ Sperms:
◉ Structure:
◈ Head: Contains nucleus + acrosome
◈ Neck: Holds centrioles
◈ Middle Piece: Mitochondrial region
◈ Tail:
■ Main Piece: Axial filament + cytoplasm
■ End Piece: Naked axial filament
◉ Special Case: Amoeboid sperm in Ascaris
❖ Fertilization:
◉ Definition: Fusion of male and female gametes
◉ Types:
    ■ External: In water (e.g., Frog)
    ■ Internal: In ovoviviparous/viviparous (e.g., Humans)
◉ Biochemical Process:
◈ Fertilizin: Glycoprotein from egg surface
◈ Antifertilizin: Acidic protein from sperm
◈ Reaction: Species-specific binding
◉ Key Events:
  1. Sperm penetration via acrosomal enzymes
  2. Formation of fertilization cone
  3. Development of fertilization membrane (blocks polyspermy)
  4. Completion of meiosis II (in vertebrates)
◉ Amphimixis: Fusion of male/female pronuclei → Diploid zygote
❖ Cleavage:
◉ Characteristics:
  1. Rapid mitotic divisions without growth
  2. Decreasing blastomere size
  3. High metabolic rate
◉ Patterns:
    ■ Radial: Blastomeres arranged radially (e.g., Echinoderms)
    ■ Spiral: Spiral arrangement (e.g., Annelids)
    ■ Bilateral: Right-left symmetry (e.g., Mammals)
◉ Types:
    ■ Holoblastic:
    ● Equal: Microlecithal eggs (e.g., Humans)
    ● Unequal: Mesolecithal eggs (e.g., Frog)
    ■ Meroblastic:
    ● Discoidal: Telolecithal eggs (e.g., Birds)
    ● Superficial: Centrolecithal eggs (e.g., Insects)
◉ Stages:
    ■ Morula: Solid cell ball (mulberry-like)
    ■ Blastula:
    ● Types:
    1. Coeloblastula (Amphioxus)
    2. Stereoblastula (Molluscs)
    3. Discoblastula (Birds)
    4. Superficial blastula (Insects)
    ● Mammalian Specialization: Trophoderm forms at blastocyst stage
❖ Gastrulation:
◉ Purpose: Forms three germ layers (ectoderm, mesoderm, endoderm)
◉ Processes:
  1. Epiboly: Ectodermal expansion
  2. Emboly: Cell migration (invagination, ingression, etc.)
◉ Structures Formed:
  1. Archenteron (primitive gut)
  2. Blastopore (absent in amniotes)
◉ Developmental Significance:
◈ Protostomes: Blastopore → Mouth (e.g., Annelids)
◈ Deuterostomes: Blastopore → Anus (e.g., Humans)
❖ Germ Layer Derivatives:
◉ Ectoderm:
  1. Nervous system
  2. Epidermis
◉ Mesoderm:
  1. Muscles
  2. Skeleton
◉ Endoderm:
  1. Digestive tract lining
◉ All Three Layers:
  1. Tympanic membrane
  2. Epithelial tissues
  3. Digestive system components