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
Concerning the presence of the nucleus what is the difference among animal and bacterial cells? Animal cells (cells of living beings of the kingdom Animalia) have an interior m

Explain the Malthus' Theory about population growth? Darwin's Theory was also based on Thomas Malthus' writings on population growth, in which he explained that populations gro

Explain primary structure of proteins The primary structure of a protein having of the order in which amino acids are bonded to one another by a peptide bond.

Explain Deficiency diseases due to vitamin C? Vitamin C deficiency in human's results in the disease called scurvy, whose symptoms include hemorrhaging (especially in the gums)

Sterility in Angiosperms Sterility in angiosperms may arise due to several causes. Either the anther may not be formed, or anthers are formed but meiosis may be abnormal. A

Flowering - Development of plant One of the major changes that occur during the life cycle of a plant is the transition from vegetative stage to the flowering stage. In this t

Matthew Meselson and Frank Stahl grew bacteria in media having either N14 or N15 for various numbers of cell divisions. DNA from the bacterial samples were isolated and spun within

Explain An important strategy of group meetings An important strategy could be to conduct small group meetings for behavioural change encouraging full participation. The group

What are the personal protective equipments for infection control? Personal protective equipments for infection control are: Protective clothing Masks Protective eyewe

History of diet nnd or  tube feeding tolerance History of diet nnd or  tube feeding tolerance: The dietitian  presents  the patient's history, which may  include presence or hi