This is an excellent book, highly enjoyable! The detail concerning the Common frog has remarkable depth, beginning with the properties of the spawn continuing to the hatching process, the life history of the tadpoles; Metamorphosis; the life of the juvenile frog; the adult frog; and circling back around to breeding information.
Much of the work is from the author's own research and Savage also draws from that of others, there are many intriguing discussions which suggest areas for new research - however being a book from 1961 it seems likely much of that may have been completed and that this is not as up to date as if it were written more recently. Regardless, with such fascinating insights and field work such as weighing to the milligram tadpoles in the field in the late 1940's it is so remarkably impressive that one must recommend it to anyone with an interest in Common frogs.
There are some aspects of this book that are of a rather technical and scientific detail, if you, like me, are not the most versed in such writing you may need to read a few sections a couple of times. Regardless, this is an excellent buy which I cannot recommend enough!