This monograph contains a review of literature dealing with the comparative physiology of the thyroid and parathyroid glands. The author, who has himself contributed widely to this field, has covered the subject adequately, describing pertinent discoveries in organisms ranging from ammocoetes to man. The hormones subserve such basic functions in the animal economy that it is not surprising to learn they are identical throughout the vertebrate phylum. A study of comparative endocrinology is thus not without value in understanding hormonal functions in the human. The author has included a bibliography of over 100 references. Although the monograph is of value primarily to the experimental endocrinologist, the internist will find it of some interest. The format and style are good; a more extensive treatment of the subject and inclusion of illustrations would have been desirable.