Which of the following lists the stages of early animal development in the correct order?

A) blastula, embryo, gastrula, zygote

B) gastrula, blastula, embryo, zygote

C) gastrula, blastula, embryo, zygote

D) embryo, zygote, gastrula, blastula

B) gastrula, blastula, embryo, zygote

Explanation:

The correct order of animal development is either gastrula < - blastula < - embryo <-zygote or zygote - > embryo - > blastula - > gastrula.

Zygote is the first cell of next generation which is formed by the fusion of gametes (ovum & sperm) from both the parents. During early embryonic developments, the very first cleavage in zygote produces two cells and now the zygote is rather termed as embryo. Further cleavages in the embryo produce another structure which resembles mulberry and therefore now the embryo is termed as morula. Repeated cleavages in morula leads to the formation of a hollow sphere of cells known as blastula. More and more cleavages in blastula finally produces another structure gastrula which is characterized by multiple layers (endoderm, mesoderm and ectoderm) of cells. Formation of primitive gut also occurs in gastrula stage.