He has a deep interest in teratology.

He is an expert in embryology, studying the developmental processes of many kinds of organisms.

He is majoring in political science at university.

I am majoring in embryology at university.

He is an expert in statistics.

He is majoring in linguistics.

He has a deep interest in astronomy.

Electromagnetism is a part of physics that studies the interaction between electricity and magnetism.

He is majoring in analysis at university.

He is an expert in bibliography and works in many libraries.