Spiral cleavage - metazoa, Biology

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.

Posted Date: 1/15/2013 1:48:34 AM | Location : United States







Related Discussions:- Spiral cleavage - metazoa, Assignment Help, Ask Question on Spiral cleavage - metazoa, Get Answer, Expert's Help, Spiral cleavage - metazoa Discussions

Write discussion on Spiral cleavage - metazoa
Your posts are moderated
Related Questions
Explain the Swab Method? Swab method is the oldest and widely used method in food and dairy industry and was developed by W.A. Manheimer and T. Ybanez in 1917. A sterile cotton

Braxy The causative agent of braxy is Cl. septicum. It usually affects lambs. The agent is a normal inhabitant of soil and is frequently found in the faeces of herbivores. Bra

Leptospirosis It is a bacterial disease that occurs in many domestic and wild animals, is endemic worldwide, but the highest incidence is in tropical and subtropical areas. Tr

Question 1) What is megalobastic anemia? Discuss briefly its lab diagnosis. How would you differentiate megaloblastic anemia from other anemias? Question 2) What is hem

different types of respiration

Food Which can be Taken in Plenty and Food to be Avoided Lastly, in the context of changing the diet, we should know the foods to be avoided and the food to be taken in plenty

List the routine treatment sequence for an implant patient. The different phases are - Preliminary treatment - Stage I surgical phase - Stage II surgery and Prosthetic

Which of the following is a false statement regarding Polymerase Chain Reaction (PCR)? A. PCR is a modified version of cellular replication that is used to amplify small amount

Q. What is Peaked T-Waves? Exercise induced increase in T-wave amplitude in V2 is quite predictive of anterior wall ischaemia (specificity = 95 percent). It appears that this m

R i n g w o r m It is also known as dermatophytosis resulting in alopecia, scab formation and ring like lesions in the affected body parts. Eti o logy: Zeop