Seminiferous tubules are units of testes. These are present in testis of frog and mammals both.
Germinal cells are sperm forming cells present inside testes. Sertoli cells are characteristic of testis of mammal, found in germinal epithelia of seminiferous tubules of testes.
These are absent in frog's testes. In mammals endocrine cells of testes are known as leydig cells in general these cells are known as imesritial cells as in frog.