Ans.: Mehlis’s glands, though also known as shell glands, do not play any role in shell-formation. They are a cluster of unicellular glands and surround the junction of oviduct, medial vitelline duct and uterus. Their secretion helps in lubricating uterus for smooth passage of eggs and in activating sperms. This secretion, perhaps, also causes release [...]
Ans.: Biradial is a combination of radial and bilateral symmetry. Ctenophores exhibit biradial symmetry. Some of the phyla formerly classified as aschelminth have anterior and radial portions.
Ans. In bilateral symmetry (also called plane symmetry), only one plane, called the sagittal plane, will divide an organism into roughly mirror image halves (with respect to external appearance only, see situs solitus). Thus there is approximate reflection symmetry. Often the two halves can meaningfully be referred to as the right and left halves.
Ans. Where the organisms resemble a pie where several cutting planes produce roughly identical pieces. An organism with radial symmetry exhibits no left or right sides. They have a top and a bottom (dorsal and ventral surface) only.
Ans. In animals, metamerism is defined as a mesodermal event resulting in serial repetition of unit subdivisions of ectoderm and mesoderm products. Endoderm is not involved in metamerism. Segmentation is not the same concept as metamerism. Segmentation can be confined only to ectodermally derived tissue, e.g., in the Cestoda tapeworms. Metamerism is far more important [...]
