Comparative suggests organisms that are more closely related have more similar embryo development. morphology embryology fossil records

Comparative embryology is the study which determines the organisms that have the same and almost identical embryo development.

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While, comparative morphology is the scientific study of organisms where their structures, physical entities and elements are identified to be similar or dissimilar. Using only simple basis of empirical observation, a scientist can detect whether two animals are of the same family or not.

Spherical shaped cell might increase the surface area and decrease the volume.