For M.sc zoology entrance, it is important that you cover the whole syllabus of bachelor's degree. Each and every topic of B.sc zoology is important for entrance.
One more thing to remember is you mainly have to focus on classification part and biochemistry part. These two covers most of the questions asked in your M.Sc zoology entrance exam.

Some of the popular books which can help you prepare for the M.Sc. entrance examinations are as follows:
1) Zoology A Complete Guide (M.Sc. Entrance Examination) (1969) by Anita Sehgal Dr (Author)
2) M.Sc. Zoology Entrance Examination by A Sehgal
3) TRB Zoology (PG) Previous Years Model Solved Papers 2017 by S. Devi Parthiban (Author).

Hope this helps.

All the best.