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

How do beings of the class reptilia classify\, Concerning the maintenance o...

Concerning the maintenance of body temperature how do beings of the class Reptilia classify? Like fishes and amphibians, beings of the class Reptilia are heterothermic animals

Slow moving waters - biota of rivers, Slow Moving Waters - Biota of Rivers ...

Slow Moving Waters - Biota of Rivers The habitat of a slowly moving part of the river is very different from the one just described. Here the water flow is comparatively slow

Describe the nature of the polymorphism, 1. DNA damage can occur spontaneou...

1. DNA damage can occur spontaneously or be induced by external factors. Describe the types of DNA damage caused by external factors and how they are repaired in prokaryotes and eu

Mucoproteins (glycoproteins), MUCOPROTEIN S (GLYCOPROTEINS) Protein...

MUCOPROTEIN S (GLYCOPROTEINS) Proteins having conjugated mucosaccharides that form viscous mucus or mucoid secretions. The gastric mucus or mucoprotein is resistant to p

Determine the membrane voltage of neuron b, Consider Neuron B in the frog c...

Consider Neuron B in the frog central nervous system whose plasma membrane has a previously unknown channel that is selectively conductive to a newly discovered tetravalent anion n

Reflex action, REFLE X ACTION - Marshel Hall discovered reflex ac...

REFLE X ACTION - Marshel Hall discovered reflex action. Best & Taylor defined it. Reflex action is functional unit of CNS. It is sudden, immediate involuntary acti

Explain the effect on minerals of the human milk, Explain the effect on Min...

Explain the effect on Minerals of the Human milk? There appears to be no relationship between dietary intake and concentrations in milk for copper, iron or zinc. Iron supplemen

What is phosphorylation, Q. What is phosphorylation? What are various biolo...

Q. What is phosphorylation? What are various biological processes in which phosphorylation plays a critical role? Phosphorylation is the name given to procedure of the addition

What is the window phase of an infection, What is the window phase of an in...

What is the window phase of an infection? How is this concept important for the test of HIV infection in blood banks? The primary immune response of the body facing any infecti

Explain the oligosaccharides (dp: 3-9) - carbohydrates, Explain the Oligosa...

Explain the Oligosaccharides (DP: 3-9) - carbohydrates? Oligosaccharides consists of short chains of monosaccharide units joined by covalent bonds. The glycosidic bond may be α

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