2. Endocrines and Populations 193 



content of the adrenals to determine whether and to what degree a stunulus 

 produces ''stress." Although the adrenals are of primary importance in 

 physiologic adaptation to changing needs, it is important not to equate 

 adaptation solely with adrenal function or to assume that the only function 

 of the adrenals is to enable an organism to meet new and sudden demands. 

 It is appropriate, especially for the mammalogist, to discuss adrenal glands 

 in some detaU because of their importance and because of the convenience 

 of using them as indices of the degree of adaptive response to particular 

 situations or stimuli. However, judgment must be used in interpreting the 

 results of measurements of adrenal function, and one must realize that 

 there are many other responses which are measured with extreme difficulty, 

 and yet others may be completely masked by extraneous factors. 



a. General morphology of the adrenal glands. The anatomy of the adrenal 

 glands is discussed in detail in many texts and papers on histology, gross 

 anatomy, and comparative anatomy. Attention is called to the books by 

 Bourne (1949), Hartman and Brownell (1949), Bachman (1954), and 

 Jones (1957) for general treatments, especially from the comparative point 

 of view. 



The adrenal glands are yellowish paired organs lying at or near the 

 anterior poles of the kidneys. Their position and form vary considerably 

 from species to species. For example, in rabbits (Stjlvilagus, Oryctolagus) 

 they are oval discoid organs closely applied to the vena cava; in wood- 

 chucks (Marmota) they are sausage-shaped and lie between the kidneys 

 and the midline, usually closer to the latter; in mice and voles of almost all 

 species they are round, oval, or pyramidal and lie approximated to the 

 poles of the kidneys; and in the bats Myotis and Pipistrellus they lie be- 

 neath a layer of the renal capsule. These examples simply serve to illustrate 

 the wide variations that occur in their gross shape and position. 



Two distinct portions of the adrenal are discernible when they are sec- 

 tioned and examined grossly: a dark reddish brown or gray central core, 

 the medulla ; and a wide outer portion, the cortex, which is usually yellowish 

 but may be gray or even translucent reddish brown, dependmg on the 

 activity of the gland. The yellow color is imparted by lipids contained in 

 the cortical cells; thus color will vary with changes in the lipid content. 

 Usually the cortex is quite wide, comprising from one-half to two-thirds of 

 the radius of the gland. However, in some of the adult soricid shrews (Sorex 

 jumeus, S. cinereus, S. palustris, S. dispar, and Microsorex hoyi) the gland 

 consists almost entirely of medulla and has a very narrow cortex only a few 

 cells wide. The extreme narrowness of the cortex is especially pronounced 

 in mature male shrews. 



The adrenal gland is surrounded by a connective tissue capsule from 

 which a stromal framework of connective tissue descends into the cortex. 



