Spiral cleavage - metazoa, Biology

Assignment Help:

Spiral Cleavage - Metazoa

In Spiral Cleavage, however, the third and fourth cleavage planes are oblique to the polar axis and the resulting blastomeres do not lie on top of one another but above the furrows between the cells. The spindles during the third cleavage are arranged in the form of a spiral, therefore, the name spiral cleavage. This type of cleavage is seen in all invertebrate except the echinoderms (i.e. in annelids, molluscs, arthropods nemertenes and polyclad planarians).

159_Spiral Cleavage - Metazoa.png

                                              Figure: Spiral cleavage showing transition from 4 to 8 to 16 cell stage

Spirally cleaving embryos are said to have mosaic or determinate form of development. This means that the organ forming regions of the egg are strictly localised in the egg from the very beginning and the fate of the blastomeres is determined early. If the blastomeres are separated, each will continue to develop up to a certain time as though it was a part of the whole and give rise to defective, partial embryos. In the early embryos an unidentified cytoplasmic factor is segregated into one of the blastomeres, the mesentoblast (this is also called the '4 d' cell) which gives rise to the future mesoderm.


Related Discussions:- Spiral cleavage - metazoa

What are the venous of the valves system, Q. What are the venous of the val...

Q. What are the venous of the valves system? What is their function? The valves of the venous system are structures inside the veins that permit blood to flow only in the norma

Characteristics of metazoa, Characteristics of Metazoa The unicellular...

Characteristics of Metazoa The unicellular protozoans are highly versatile and successful organisms that show remarkable organization and division of labour within the confine

Which harmone is not associated with male reproduction, Which of the below ...

Which of the below is NOT hormone associated with male reproductive physiology: a) Prolactin b) Testosterone c) Interstitial hormone d) Follicle-stimulating hormone

Determine the causal factors of nervous system, Determine the Causal factor...

Determine the Causal factors of nervous system Although, the brain and spinal cord are surrounded by tough membranes, enclosed in the bones of the skull and spinal vertebrae, a

Isomerization of citrate, Isomerization of  citrate Isomerization of ...

Isomerization of  citrate Isomerization of  citrate:   In  this  step,  citrate is isomerized to isocitrate by aconitase which has iron-sulphur centre as  its prosthetic  grou

Leptontene and zygotene, Leptontene: The chromosomes becomes visible,...

Leptontene: The chromosomes becomes visible, shorten and thick. The size of the nucleus increase. The homologous chromosomes start getting closer to each other. Z

Why is a leguminous crop rotation used in agriculture, Q. Why is a legumino...

Q. Why is a leguminous crop rotation used in agriculture? The Leguminous crop rotation and other crop rotations are used in agriculture for the reason that in these plants many

Could you survive on a diet which contained no carbohydrate, Could you surv...

Could you survive on a diet which contained no carbohydrate?   It should be possible to survive without carbohydrate as energy can be obtained from fats and proteins.

Define role of food industry, Define Role of Food Industry? Publication...

Define Role of Food Industry? Publications of major trade associations; industry standards; structure of the food industry; international food corporations; information on alli

What are bacteria, What are bacteria? Bacteria are unicellular and prok...

What are bacteria? Bacteria are unicellular and prokaryotic beings. Bacteria have simple organization; they present an , plasma membrane, external cell wall, circular DNA withi

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd