dev bio frog

• 7mm Frog Embryo

  • Well-formed external gills
  • Functional heart
  • The embryo has changed its shape and has become a tadpole
• Features of Tadpole

  • The eggs of the frog hatch in the water and release free living herbivorous larva
  • The larva measures about 5-7 mm in length
  • The body of the larva is differentiated into a head, a body proper and a tail with fin
  • The larva contains a head with mouth, sucker, external gills, rudiments of eye and olfactory pits which are visible externally. The larva also contains the gut, anus and myotomes (muscles) which are present internally
  • Mouth of larva bears horny jaws or teeth
  • Three pairs of external feathery gills can be seen. These act as the functional respiratory organs
  • Tail is long and bears the tail fin on its ventral and dorsal surface
  • The herbivorous larva feeds on vegetation and has a coiled intestine
  • The larva metamorphoses into an adult amphibians (which live both on land and water) frog
• Features of Transverse Section of Tadpole through the Eye Region

  • The paired eyes in the frog tadpole develop very early and are of ectodermal origin. They are the most conspicuous and protuberant structures of the tadpole
  • Eyes develop from the optic vesicles which originate from a pair of diverticula given off from the prosencephalon of the brain on each side
  • A transverse section (T.S.) of the tadpole through the eye region shows the forebrain in the centre on the dorsal surface
  • The paired eyes are seen on the lateral sides of the brain and are composed of lens, sensory layer of retina and eye muscles
  • The single pharynx lies in the centre of the transverse section
  • Hyoid arch lies just below the pharynx in the transverse section
  • The paired palatoquardate bars are placed dorsal to the pharynx on each lateral side
  • Meckel's cartilage is present on each lateral side of the pharynx
  • Other structures seen in the section are jaw muscles, trabeculae, epidermis and connective tissue
• Features of Transverse Section of Tadpole through the Auditory Vesicles

  • The paired ears (auditory vesicles) develop as a pair of auditory pits from the epiblast on the lateral sides of the hind brain
  • The auditory vesicles develop at an early tadpole stage and are found on the dorso lateral side of the section, below the hind brain
  • The auditory pits become vesicle-like and enclose the middle ear. The semicircular canals develop as outgrowths from the wall of the auditory vesicles
  • The single median, medulla oblongata of the hind brain encloses the fourth ventricle and is located in the middorsal region of the section between the two auditory capsules
  • The notochord lies below the medulla oblongata
  • The branchial chamber containing the laryngeal chamber lies below the notochord and auditory vesicles
  • The pericardial cavity enclosing the developing auricle (atrium) and ventricle of the heart is located on the ventral side of the section, below the laryngeal chamber
• Features of Transverse Section of Tadpole through Head and Gill Region

  • The median medulla oblongata enclosing the fourth ventricle lies in the middorsal position
  • The paired membranous labyrinth are present on both the lateral sides of the medulla oblongata
  • The notochord lies just below the medulla oblongata
  • The pharynx lies in the centre of the section
  • Larynx is seen in continuation with pharynx
  • The heart enclosed in the pericardium is seen just below the larynx
  • The branchial arches and internal gills are present on the lateral sides of the pericardium
  • The lateral dorsal aorta is located above the pharynx
  • Lymphatic spaces lie on both the lateral side
• 10mm frog embryo

  • Frog embryo forms after the development of gastrula where its three germ layers are developed
• The three germ layers

  • Ectoderm
  • Endoderm
  • Mesoderm
• Ectoderm

  Mostly responsible for the development of nervous system followed by sense organs
• Endoderm

  Responsible for the development of the gut that extends from buccal cavity to the anus
• Mesoderm

  Responsible for the development of urogenital, circulatory, arterial and venous system
• Ectodermal Derivatives of the 10 mm Frog Embryo

  • The development of the nervous system starts from the neural tube and forms Prosencephalon, Mesencephalon, Rhombencephalon and the Spinal cord after four weeks of development
  • The Prosencephalon, after one week, will develop to Telencephalon and Diencephalon
  • Telencephalon will then form the Neopallium, Corpus Striatum and Archipallium
  • The Diencephalon will also form the Thalamus, Hypothalamus, Infundibulum, and Epiphysis
  • Mesencephalon will then form the Superior and Inferior colliculi, Tegmentum, and Cerebral peduncle after four weeks of its development
  • Rhombencephalon will form into Metencephalon and Myelencephalon after one week of its development
  • Metencephalon will then form the Cerebellum and Pons after two weeks of development
  • Myelencephalon forms the Medulla
  • Spinal cord have no further development but it will continue to grow by extending its nerve fibers
  • Sense Organs begins to form upon the development of the brain which is the formation of the Eyes and Ears. Olfactory organs, responsible for the sense of smell
  • The Cartilages mainly the Chondrocranium and Splanchnocranium also developed
• Endodermal Derivatives of the 10 mm Frog Embryo

  • The endoderm derivatives include the epithelia of the gut that extends from buccal cavity to the anus
  • Developments occurred in Endoderm includes: Branchial Region, Respiratory System, & Digestive System
  • The Branchial Region were consist of mesenchyme that were separated from each other by transverse dimensions of the gut that produce a series of outwardly-directed pockets on each side called Pharyngeal Pouches
  • The Respiratory System starts as a ventral diverticulum which is the Laryngeatracheal Groove and this at this stage the respiratory tract starts as a tube ventral to the pharynx
• Mesodermal Derivatives of the 10 mm Frog Embryo

  • Mesoderm is divided into three differentiated parts: Epimere, Mesomere, & Hypomere
  • This differentiated parts developed into Urogenital, Circulatory, Venous, & Arterial System
  • The dorsal epimere and middle mesomere forms into nephrotome while ventral hypomere forms into lateral plate mesoderm