Already have an account? Get multiple benefits of using own account!
Login in your account..!
Remember me
Don't have an account? Create your account in less than a minutes,
Forgot password? how can I recover my password now!
Enter right registered email to receive password!
Colonial Theory - Metazoa
This is the most popular theory on the origin of Metazoa. The idea was conceived by Haeckel (1874) modified by Metschnikoff (1886) and revived by Hyman (1940). This theory considers the flagellates to be the most probable ancestral group of metazoans. For support of this theory the following evidences are cited:
1) Flagellated spermatazoa occur throughout the metazoan series.
2) Monoflagellated cells (with a single flagellum) are also common in lower metazoans (especially among sponges and coelenterates).
3) True sperms and eggs (feature of metazoans) are present in phytoflagellates.
4) Phytoflagellates also display a type of colonial organization that could have led to a multicellular construction. In fact, differentiation between somatic and reproductive cells has been attained in Volvox. Although Volvox is often used as a model for the flagellated colonial ancestor, it is not the likely ancestor of metazoans. Ultrastructural evidence points to the choanoflagellates (a small group of animal like flagellates) as the probable ancestor. Choanoflagellates have mitochondria and flagellar structures very similar to those in metazoan cells. Also choanocytes i.e. cells with a collar of microvilli are found in a number of groups of metazoans notably the sponges.
What is the physiological cause of the syndrome known as cretinism? Cretinism is caused by chronic deficiency of the thyroid hormones (T3 and T4) during childhood. The chronic
What are the main functions of (a) the basal (Malpighian) layer, (b) the cornified layer of the skin? (a) The basal (Malpighian) layer makes new skin cells and the pigment
what are the general characteristicss of porifera
Q. What are the so-called "good" and "bad" cholesterol? Lipoproteins are complexes made of lipids (cholesterol and triglycerides) and proteins. The lipoproteins present differe
Chromosomes and Their Organization During division phase , the duplicated chromatin fibres become extremely shortened (= condensed), by coiling and folding ,into short
Algae Advantages a) Produces proteins which have almost all the Essential Amino acids. b) Rich in tyrosine and serine, low in sulphur containing amino acids.
What are the three major groups into which mammals are divided? The three groups into which mammals are divided are: monotremes (or prototherian, e.g., platypus), marsupials (o
DIANCEPHALO N - Less visible. Occupies only 1% of brain's volume. Its lumen is diocoel or III ventricle. Roof is epithalamus . On it pineal body is present. Fl
Determine the uses of Electrical Recording - Brain function We can also learn about brain function by recording its electrical activity. In electroencephalography (EEG) and the
lesson plan practical requirements
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!
whatsapp: +1-415-670-9521
Phone: +1-415-670-9521
Email: [email protected]
All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd