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

Zoonoses disease- colibacillosis, Colibacillosis Colibacillosis is caused ...

Colibacillosis Colibacillosis is caused by different strains of Escherichia coli. The disease mainly affects children and travelers. Organisms grow in gut and produce toxin. It ma

Differentiate between glycogenesis and glycogenolysis, Differentiate betwee...

Differentiate between glycogenesis and glycogenolysis. The synthesis  of glycogen in liver and muscle  is  called glycogenesis.  The breakdown of glycogen in the liver (glycoge

General procedure of titration - nutritional biochemistry, Define General ...

Define General procedure of titration - Nutritional  Biochemistry? In general a titration requires that we add precise amounts of the known titrant to the unknown analyte or ti

Calamity & emergency management - nutritional needs of human, Define Calami...

Define Calamity and Emergency Management - nutritional needs of humans? During past many years, we have seen, as well as, realized -that natural calamities strikes countries, b

Define effect of protein deficiency during pregnancy period, Define effect ...

Define effect of Protein deficiency during pregnancy period? The effects of protein deficiency during pregnancy are difficult to separate from the effects of caloric deficit, s

Reduction in the birth rate, State three conditions in a society which coul...

State three conditions in a society which could contribute to a reduction in the birth rate. Birth rate might be decreased by (i) later marriages (as smaller families), (

Mode of nutrition , What is the mode of nutrition in fish,human,amoeba,scor...

What is the mode of nutrition in fish,human,amoeba,scorpian & toad ?

What is mitosis, What is mitosis? What is the importance of mitosis? Mi...

What is mitosis? What is the importance of mitosis? Mitosis is the process in which one eukaryotic cell separates into two cells identical to the parent cell (generally identic

Nutrition, Why is holophytic nutrition a mode of autotrophic nutrition

Why is holophytic nutrition a mode of autotrophic nutrition

Management of diabetes, By now you know that diabetes cannot be cured but c...

By now you know that diabetes cannot be cured but can be treated so that an individual leads a normal life. Patients who maintain their blood glucose levels within the normal range

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