Question

Cleidoic egg is found in
A. Birds
B. Reptiles
C. Insects
D. Both A and B

Answer 1

Cleidoic eggs are a characteristic of amniotes which is characterized by the presence of a protective shell over the eggs. It is permeable to air and can be flexible or calcareous. Such eggs are usually not laid in the water.

Complete answer:
- Cleidoic eggs enable reproduction out of the water which is a step forward in the course of evolution from amphibians to reptiles. Such eggs contain all the nourishment that is required by the embryo to develop into hatching.
- Calcareous eggshells play an important role in preventing any kind of desiccative stress. Such eggs undergo internal fertilization. After the eggs are laid, they are protected and provided favorable temperatures until they hatch.
- Reptiles and birds lay cleidoic eggs as they are land animals.
- Reptiles have eggs that are rubbery and white.
- Birds even lay unfertilized eggs.

Therefore, the correct answer is (D) Both A and B.

Note:
The eggs are classified into four categories based on the amount and distribution of yolk in them. These are Alecithal, Microlecithal, Mesolecithal, and Megalecithal/ Macrolecithal.
- Yolk is the reserve food material in the cytoplasm of the egg.
- It may be formed of phospholipids, proteins, lipids, and carbohydrates.
- The process of formation of yolk and its deposition in an egg is called vitellogenesis.
Eggs are also classified based on the distribution of the yolk. These are Isolecithal (uniform distribution of yolk throughout the cytoplasm), Telolecithal (eggs with their yolk toward one pole), and Centrolecithal (eggs with their yolk concentrated in the center of the cell, surrounded by the cytoplasm).