Question

Polylecithal egg of reptiles, bird and monotremes are also called “cleidoic” egg because these
A) Have calcareous shell and other membrane
B) Are an adaptation to terrestrial life
C) Have self sufficient food, water and salt
D) None of the above

Answer 1

Hint:On the basis of distribution of yolk, egg is divided into homolecithal egg, telolecithal and centrolecithal egg. On the basis of the amount of yolk, the egg is grouped into alecithal/ microlecithal, mesolecithal and macrolecithal/polylecithal.

Complete answer:
->In the polylecithal egg, the amount of yolk content is very large.
->The polylecithal eggs are found in prototherian mammals, reptiles, birds.
->Homolecithal eggs are the eggs in which the total amount of yolk present is small but uniformly distributed throughout the cytoplasm.
->Homolecithal eggs are found in sea urchin, amphioxus, tunicates and mammals
->There are two types of eggs on the basis of shell- cleidoic eggs and non-cleidoic eggs.
->Cleidoic eggs are surrounded by hard covering or shell.
->Cleidoic eggs are found in reptiles, birds.
->Cleidoic eggs have a protective shell. This shell is porous to air and the shell can be flexible or calcareous.
->The cleidoic eggs enable reproduction out of and often away from water. It is a characteristic of birds and reptiles.
->Centrolecithal egg- egg of many arthropods and some coelenterates are called centrolecithal. They are relatively large and have a great amount of yolk.

Hence the correct answer is option ‘A’.

Note:Eggs are laid by female animals of different species such as birds, reptiles, amphibians, mammals and fish. On the basis of development eggs are classified into mosaic eggs and regulative eggs. Microlecithal type of egg is found in amphioxus and tunicates.