Question

“Homolecithal” egg are found in
A. Petromyzon, tunicates and chondrichthyes
B. Amphioxus, fish and amphibia
C. Amphioxus, tunicates and mammals
D. Birds, reptiles and monotremes

Answer 1

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.

Complete Answer:
- Very little amount of yolk present is uniformly distributed throughout the ooplasm in the homolecithal egg. Homolecithal eggs are found in echinoderms, amphioxus and mammals.
- Telolecithal eggs contain moderate or large quantities of yolk and the distribution of yolk is not uniform.
- Centrolecithal eggs of many arthropods and some coelenterates are called centrolecithal. They are relatively large and have a great amount of yolk.
- When the egg contains no yolk it is called an alecithal egg.
- Cleidoic egg contains a thick and hard outermost shell. Cleidoic egg is a terrestrial adaptation. Example –birds, reptiles.
- Non- cleidoic eggs are found in all viviparous animals and in oviparous animals which lay eggs in water.
- 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.

So the correct answer is Amphioxus, tunicates and mammals.

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.