68 E. V. COWDKY 



adrenal tissife and the epinephrin secreting poison glands of the toad, 

 which also exhibit the chromaphil reaction (Shipley), has not been 

 ascertained. 



Quantitative Relations. The relative amounts of the two tissues have 

 not been accurately studied in phylogeny. Elliott and Tuckett point out 

 "that the. lower the animal in the vertebrate, or at any rate, in the 

 mammalian series, the greater is the relative development of the cortex." 



Constancy of Cell Types. The different cell types are remarkably 

 constant throughout the vertebrate scale, Rana esculent a alone containing 

 a type of cell which is strongly acidophilic and which seems to be without 

 counterpart in other forms. 



Histology 



The Cortex. Zones of the Cortex. In the cortex the cells are ar- 

 ranged in three groups called, from without inwards, the 'zona glomerulosa, 

 the zona fasciculata, and the zona reticularis. These layers are subject to 

 considerable variation in different animals, being much more distinct in 

 some than in others, Mulon believes that in the guinea pig the glomerular 

 zone is germinative and that the cells in it continue to multiply through- 

 out life. This idea is supported by the studies of Graham, who believes 

 that the zona glomerulosa and the outer cells of the zona fasciculata are 

 the growth centers for regeneration in the adult. Unfortunately we have 

 no reliable data for man on which to base an opinion. There are no trust- 

 worthy indications of a division of labor in the zones of the cortex with 

 respect to either growth or secretion (Fig. 6). 



Cell Types. (1) Clear Cells Their Inclusions: (a) Lipoid Sub- 

 stances. Two types of epithelial cells are often described in the cortex, the 

 clear cells and the dark cells, depending upon their appearance in fixed 

 and stained preparations. The clear cells in the guinea pig are the most 

 numerous. They contain an abundance of rather large, fatty, spherical 

 droplets which are highly refractile, stain with Sudan III, sometimes 

 blacken with osmic acid, and are very soluble in essential oils. Their exact 

 chemical nature remains undetermined. There is no reason to believe that 

 they are the same in different species. They are often present in variable 

 amounts in the different zones. According to Elliott and Tuckett, they 

 are absent in sheep. These granules are dissolved out in ordinary prepara- 

 tions, thus giving a vacuolated appearance to the cells (illustrated in Fig. 

 7). Doubly refractile lipoid granules are also present, which produce 

 myeline forms when liberated from the cells. Thyroid feeding is thought 

 to bring about a reduction in the amount of lipoid. Ascoli and Legnani 

 claim that the lipoid is increased by hypophysectomy (citation from 

 Schiifer). 



