The experimental work of many investigators has shown that castration of the male rodent results in the involution of the accessory reproductive organs. This has been shown to be the case particularly in the rat, mouse, thirteen-lined ground squirrel, and in part in the guinea pig. With the involution of these glands cytological and histological changes have frequently been rapid and diagnostic following loss of the normal hormone supply. The accessory organs studied in this report are the long, tapering seminal vesicles, the compound tubular anterior, middle and posterior lobes of the prostate and the ductus deferens. Cowper's gland was not studied because Heller ('32) found that it underwent retrogression following castration.
An earlier paper (Sayles, '39) reported that in the young normal guinea pig the accessory reproductive organs gradually increase in weight up to 30 days of age following which there is a marked acceleration in rate of the weight increase. Spermatozoa do not appear in the testes until 77 days of age. The accessory organs show adult histological characteristics at the age of 30 days and tend to give the characteristic adult castrate response in animals castrated after this age.
This investigation has been aided by a grant from the Rockefeller Foundation t o The University of Chicago. The author desires to express his appreciation to Dr. Carl R. Moore for his generous help and guidance during the course of the investigation.