Which of the following is the correct match?
A. Centrolecithal egg – insect
B. Megalecithal egg – eutherian mammals
C. Microlecithal egg - reptiles
D. Alecithal egg – birds

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Hint: Many arthropod organisms have centrolecithal eggs. The eggs differ from each other by the position of yolk in the cytoplasm of the egg. These types of eggs are large and have a great amount of yolk.

Complete answer:
> Megalecithal eggs are also called Polylecithal and egg laying mammals like Birds, Reptiles etc lay these eggs. These eggs are large in size as the name suggests and also have large quantities of yolk in them. These eggs are also termed as Macrolecithal. Eg are crocodiles, snakes, sparrows etc.

> Microlecithal eggs contain small amounts of yolk as the name suggests are called microlecithal types of eggs. Amphioxus, Tunicates are microlecithal egg laying organisms. These eggs are also called oligolecithal eggs. Eg are sea squirts, sea pork, sea tulip etc.

> Centrolecithal eggs are the eggs which contain nucleus at the centre of the yolk and have a great amount of yolk and it is an elongated type of egg. Eggs of arthropods and some coelenterates are centrolecithal eggs. Fine strands of cytoplasm occupied by zones of nucleus are extended from the peripheral layer. Eg are spiders, beetles, butterflies etc.

> Alecithal eggs do not contain yolk in them and just have cytoplasm in them. Eggs of eutherian mammals have alecithal eggs. Eg. Whales, elephants, sheep etc.

Hence, The correct answer is option (B).

Note: Centrolecithal eggs are classified based on distribution of yolk in the egg whereas other options like Megalecithal, Microlecithal, Alecithal are classified based on the amount of yolk in the egg. Other types of eggs based on distribution of yolk are Isolecithal eggs and Teolecithal eggs. Therefore, egg classification should be kept in mind before choosing an answer.