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

Precursors for gluconeogenesis, Glycerol can act as a substrate for glucose...

Glycerol can act as a substrate for glucose synthesis by conversion to dihydroxyacetone phosphate and an intermediate in gluconeogenesis.  In  order  for citric  acid  cycle pyruva

Explain false left ventricular aneurysm, Explain False Left Ventricular Ane...

Explain False Left Ventricular Aneurysm? False Left Ventricular Aneurysm :  False aneurysm develops after acute rupture of an infarct. It is usually fatal, but a few survive

Explain lyme disease, Explain Lyme disease The disease - About 70-80% o...

Explain Lyme disease The disease - About 70-80% of patients infected by B. burgdorferi develop the characteristic skin lesion, erythema migrans, which occurs at the site of the

What are the main sources of mercury pollution, Q. What are the environment...

Q. What are the environmental harms caused by mercury pollution? What are the main sources of mercury pollution? The Mercury is a metal that when present in the water of rivers

Why is this area more vulnerable to damage than others, A small family was ...

A small family was traveling in the car when a minor accident happened. The children in the back seats were wearing lap belts, but still sustained numerous bruises about the abdome

Define absorption, Define Absorption, Storage and Elimination of Pyridoxine...

Define Absorption, Storage and Elimination of Pyridoxine? Pyridoxine, pyridoxal and pyridoxamine (along with their phosphorylated forms) occur in plant and animal foods. The ph

What is endocrine system explain, What is Endocrine System explain ? Th...

What is Endocrine System explain ? The endocrine system consists of glands, organs that secrete hormones. Endocrine glands are tissues that produce secretions within the body,

What is sports nutrition, What is Sports Nutrition? Sports nutrition i...

What is Sports Nutrition? Sports nutrition is a discipline which applies principles derived not only from nutritional but also biochemical and physiological scientific knowled

Inotropic agents, All currently available inotropic agents act to increase ...

All currently available inotropic agents act to increase Ca 2+ for activation in both normal and failing myocardium (Hurst). The use of inotropic agents in the treatment of CHF is

What is meant by concentration gradient, What is meant by concentration gra...

What is meant by concentration gradient? Is it correct to refer to "concentration gradient of water"? Concentration gradient is the difference of concentration of a substance

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