2. Endocrines and Populations 197 



suhterraneiis) , and shrews (Sorex araneus and Crocidura russula) (Delost, 

 1951, 1952a, 1954, 1957; Delost and Delost, 1954, 1955), but there is some 

 question whether the X-zones of these species are entirely analogous to the 

 X-zones of the house mouse. Delost (1954, 1956b) reports that cortisone 

 involutes the so-called X-zone of voles, which is a response not seen in 

 house mice. The X-zone of the shrew behaves like that of the house mouse 

 with respect to its involution, but apparently has not been subjected to 

 critical experiments in the laboratory (Delost, 1957). The X-zone consists 

 of cords of small, deeply acidophilic cells with intensely basophilic nuclei 

 and which are about one-half the size of those of the zona fasciculata 

 (Howard, 1927; Deanesly, 1928; Jones, 1949a, b, 1950, 1957; Benua and 

 Howard, 1950) . The cytoplasm of these cells, besides being more acido- 

 philic than those of the fascicular cells, is unvacuolated ordinarily and 

 lacks the sudanophilia of the other zones of the adrenal cortex (Jones, 

 1957) . Criteria for critically distinguishing the X-zone have been reviewed 

 by Benua and Howard (1950) and Holmes (1955). The uniqueness of this 

 zone rests on the fact that it is involuted by androgens and appears to de- 

 pend on pituitary luteinizing hormone for its maintenance (Howard, 1927, 

 1959; McPhail and Read, 1942a, b; McPhail, 1944; Waring, 1942; Jones, 

 1949a, b, 1950, 1952, 1957). The function of this zone, if there is a specific 

 function, is unknown. The so-called X-zone of voles which has been de- 

 scribed by Delost (1951, 1952a, 1954;) and Delost and Delost (1954, 1955) 

 reappears after castration or after the hibernal periods of sexual inactivity 

 in the males and persists through gestation and lactation in the females, 

 and in these respects it differs markedly from the X-zone of house mice. 

 This zone may confound the use of adrenal weight as an index of increased 

 cortical activity in the house mouse (Christian, 1956) and other species 

 which possess it, but it provides a useful measurement for determining 

 histologically the onset of androgen production, therefore puberty, in male 

 house mice (Christian, 1956). A poorly defined X-zone has been described 

 in mature nulliparous female hamsters, but not in males (Holmes, 1955), 

 differing from the X-zone of house mice in this respect. It is likely that an 

 X-zone will be described for other species when enough material from all 

 age groups of both sexes has been critically examined, and that a variety of 

 manifestations of this zone will be found. 



The morphology and size of the adrenal cortex varies with its functional 

 status (see also discussion under reticularis) . The cortex undergoes rapid 

 hyperplasia and hypertrophy in response to stimulation by adrenocorti- 

 cotropin (ACTH) from the anterior pituitary. At first there is a rapid 

 diminution in the size and number of lipid vacuoles, ascorbic acid, and 

 cholesterol of the cortical cells (Sayers and Sayers, 1949). The vacuoles 

 soon increase in number and size, providng the stimulation is not too 



