2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



chromaphil cells are seen as groups or islands among the strands of 

 the cortex. It is interesting to note that this embryonic condition of 

 man is quite similar to the adult condition in some reptiles and birds. 



Different investigators have claimed to have found structures that 

 might be called adrenals in various invertebrate animals. It seems 

 doubtful if these claims can be substantiated, at least for the cortex. 

 According to Swale Vincent ( 1 1 ) the cyclostomes are the lowest 

 chordates in which adrenal structures are certainly known to be 

 found. In the various vertebrate classes the adrenals are, of course, 

 variously developed. In the selachians, for example, the region 

 known as the cortex in man is represented by a median, elongated 

 body, the inter-renal, lying between the kidneys ; while the medulla 

 of the human adrenal is represented by a series of small paired masses 

 of chromaphil tissue closely associated with the sympathetic ganglia, 

 called by Balfour the " suprarenals." The Amphibia, as in other 

 ways, exhibit a somewhat transitional condition in which the close 

 association of the chromaphil or medullary tissue with the sympa- 

 thetic nervous system is partially lost. 



In Reptilia and Aves, as has been said, the chromaphil penetrates 

 the inter-renal or cortical mass without forming the definite central 

 mass known in the Mammalia as the medulla. 



In the alligator, Alligator mississippiensis, the adrenals are yellow- 

 ish, elongated bodies, between and anterior to the kidneys ; they are 

 closely associated with the anterior two thirds of the gonads and 

 with the aorta and the post caval vein. 



Plate I, figure i, represents a transverse section through the 

 adrenals {ad), and the adjacent ovaries (o). In this region the ad- 

 renals are somewhat circular in section, in other regions they are 

 flattened. They are united with the ovaries (o), and the dorsal aorta 

 {ao), by a thick mass of connective tissue which is indistinctly differ- 

 entiated into a surrounding capsule (f), for each gland. The inter- 

 columnar spaces in the glands here figured were not as distinct as in 

 the gland shown in the following figure and are not indicated. 



The microscopic structure of the adrenal is shown in figure 3 

 (pi. i), which was drawn under a camera lucida, with a magnification 

 of about 500 diameters. 



As noted above, the cortex and medulla are not sharply segregated 

 into two regions as in the mammals, but the latter is seen as scattered 

 groups of cells, chiefly in the interspaces between the strands or 

 columns of the cortex. According to Vincent the conditions in Croco- 

 dilia and birds are " almost identical." 



