Extirpation of the pro- and mesoadenohypophysis was performed before and during sexual maturation in order to evaluate the influence of the hypophysis on mobilization of body tissue during starvation and on sexual development, both with respect to initiation and maintenance of the processes involved. Mobilization of tissue from the intestine and the body wall was examined in normal lampreys, and a correlation between reduction in length of the body and mobilization of body tissue was established. The mobilization was slow until shortly before sexual maturation and then rapid, most pronounced in females. Lampreys hypophysectomized in January, before sexual maturation, continued the slow reduction in length and often survived for a long time after the normal controls had died. Some of the lampreys operated in March, during sexual maturation, continued the rapid reduction in length and died in the same period as control lampreys, whereas others stopped the rapid reduction in length and survived for a long time. It is suggested that starvation may be a major cause of natural death after spawning, and that hypophysectomized lampreys survive because of a slower depletion of body tissue as apparent from the slower rate of reduction in length. The concentration of glucose in blood was about 30 mg/100 ml in hypophysectomized and in immature lampreys. After sexual maturation in normal lampreys the values rose significantly, especially in females. Growth of the ovary was accelerated during sexual maturation, and a conspicuous granular layer consisting of big, well-separated cells laden with mucopolysaccharide developed in the vegetative end of the egg. This layer did not develop in females hypophysectomized before sexual maturation. In females hypophysectomized in March, the cells of the granular layer formed a continuous layer at death in those females in which ovulation had not taken place. It is suggested that the granular layer is involved in the process of ovulation. Spermiation and ovulation never occurred in lampreys hypophysectomized in January. In males operated in March spermiation occurred in all, but sometimes with a considerable delay and accompanied by only slightly developed secondary sex characteristics. In females hypophysectomized in March only one-third ovulated, and always shortly after the operation. Secondary sex characteristics never developed in lampreys hypophysectomized in January. In males hypophysectomized in March, their development stopped or regressed. In females hypophysectomized in March, they continued to develop for some time. © 1969.
