embryogenesis in silkworms

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Assignment On Embryogenesis COMPILED BY K.Ragunath BSA-06-263

Embryogenesis ? ? : 

Embryogenesis ? ? Developmental process that usually begins once the egg has been fertilized. Why? To identify suitable stages for refrigeration. To know about initiation, continuation & termination of diapause. Device strategies for long term cold storage. To identify when diapause terminates.

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EMBRYOGENESIS

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Fertilization Sperm nucleus + egg nucleus (syngamy) = diploid zygote  ( EMBRYO) – 2 hr@ 250 C Cleavage Nucleus divides mitotically to form many which lie in polar plasm ( meroblastic).

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Blastoderm formation (12 hr) Cleavage nuclei migrate through the yolk toward the perimeter of the egg.   They settle in the band of periplasm to form individual cells. Germ band formation (24 hr) Blastoderm cells in the ventral side of egg divides & collect to form lamelliform structure called ventral plate Ventral plate further thickens to form germ band which later sink inside the egg – Daruma stage. A membraneous layer forms two folds around the germ band called serosa (entire surface) & amnion ( ventral surface)

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A narrow groove forms on germ band As the germ band enlarges, it begins to lengthen and fold into ectoderm & endoderm. Mesoderm arise from lower layer of ectoderm There are 18 embryonic segments in silkworm To attain uniform hatching the longest stage of embryo should be kept at 2.50 C ORGANOGENESIS Koembryo – 36 hr Spoon shape embryo enlarge as a tube with a small aperture blastophore . The embryo diapause with the close of blastophore.

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Otsu –A stage: It is swelling of cephalic lobe Otsu –B stage: It is distinct depression stage. Hei - A stage: body becomes long & slender cephalic lobe is distinct 1st 4 segments form head, next 3 segments form abdomen & last 11 segments form thorax Hei - B stage: Development of cephalic embryo upto 80% Period of shortening & organ formation Embryo expands in girth & shortens , segmental appendages develops distinctly. Ectoderm forms fore gut & hind gut , endoderm forms midgut. Alimantary canal, head, thoracic legs , abdominal appendages are formed. Bandelling stage

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Eye spot stage (8th day) Bristles grow around body surface Dark pigmentation around mouth & head which can be seen through egg shell as blue spot Head pigmentation Blastokinensis It is an active movement of embryo from the ventral to the dorsal side of the egg and at the same time revolves 1800 on its long axis

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Blue egg stage Whole body of the embryo turns black due to the development of body pigments It appears bluish – black through egg shell Egg should be cold stored Hatching Eggs starts hatching within 24 hours of blue egg stage. Embryogenesis ends when the yolk's contents have been consumed. The immature insect is fully formed and ready to hatch from the egg

Reference : 

Reference Comprehensive sericulture - G .Ganga Introduction to sericulture - S.Ganga & J.Sulochana Chetty http://www.seriinfo.@10% html. http://www.seriuniv.com http://www.seriagro@20%.html See you….