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

Determine the proecss of contrast sense, Contrast sense Sense of contr...

Contrast sense Sense of contrast is the ability to perceive slight changes in luminance between regions which are not separated by definite borders. This is as important as to

Determine the testing for albumin in urine, Determine the Testing for Album...

Determine the Testing for Albumin in Urine Acetic Acid Test About 2 - 8 mgm/dl of protein is excreted in urine which is not usually detected by routine test. The testing o

Introduction to meat products, Meat products Meat is an important commo...

Meat products Meat is an important commodity in the diet of people in view of its complimentary role in balancing the diet with rich source of amino acids, vitamins and mineral

What is the logic of the transfusional compatibility, What is the logic of ...

What is the logic of the transfusional compatibility concerning the Rh blood group system? The Rh + donor can only donate blood to the Rh + recipient. The person that lacks t

Annelids - regeneration in invertebrates, Annelids - Regeneration in Invert...

Annelids - Regeneration in Invertebrates Between the segmented worms both the polychaetes and oligochaetes have remarkable powers of regeneration. Leeches totally lack this ca

Tongue grafting, Tongue grafting Top of the stock is cut diagonally ...

Tongue grafting Top of the stock is cut diagonally and in an upward direction. Scion is cut diagonally in downward direction. A second cut is given from above downwards,

What is the meaning of food exchanges, What is the meaning of Food Exchange...

What is the meaning of Food Exchanges Food exchanges mean grouping of foods in which the specified amount of all the food provides approximately equal amounts of carbohydrate,

Explain the conveyor (or band) dryers, Explain the Conveyor (or Band) Dryer...

Explain the Conveyor (or Band) Dryers? In the conveyor (or band) dryer, the product is distributed on a moving belt, typically of a perforated plate, that passes through a tunn

Before purchasing - nursing software, Before Purchasing  Ideally it...

Before Purchasing  Ideally it's wise to buy a readymade software with options to further customize it to suit your managerial functions.   A totally Custom-made softwar

Airway management - respiratory failure, Airway Management To improve...

Airway Management To improved ventilation, suctioning, IPPB, Ultrasonic mist therapy and postural drainage with clapping and vibrating are all employed to halt the progress o

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