50 SOURCES OF KINETIC AND METABOLIC HORMONES 



fine granules only, and have little affinity for any cytoplasmic 

 stains. In at least some of the higher vertebrates, and especially in 

 such mammals as the cat and dog, two other types of cell can also 

 be distinguished in the islet tissue. Of these, the alpha (a) cells 

 secrete the diabetogenic hormone glucagon (Table 5); they 

 contain large granules that stain bright red with Mallory-azan 

 stain, but their cytoplasm also has little affinity for any stains.The 

 D type of cell in the islets stains blue in the same preparation, 

 but its function is unknown (Fig. 2-146; Maximow and Bloom, 

 1942). 



2.3 Mesodermal sources in Vertebrata 



Metabolic hormones secreted by mesodermal sources have so 

 far only been found in vertebrates. These come from the adrenal 

 cortex and its homologue, the interrenal tissue. Other hormones 

 from the mesoderm are all morphogenetic in their actions, or 

 predominantly so; their sources, including the source of pro- 

 gesterone (despite the possible kinetic activities that have been 

 attributed to this hormone in § 4.12), will be described in Part II. 



2.31 endocrine gland cells derived from 

 coelomic epithelium 



In all vertebrates the coelomic epithelium in the region of the 

 kidneys gives rise to characteristic yellow gland cells, filled with 

 fat and secreting cortical sterolic hormones. The cells are homolo- 

 gous in all classes; but they are differently named according to 

 their positions. In fish they often retain their median position 

 between the kidneys, where they form interrenal tissue, or they 

 may become paired, as in the perirenal organs of Dipnoi. In the 

 tetrapods the tissue forms the adrenal cortex; it is always paired, 

 lies in front of the kidneys, and becomes closely associated with 

 the adrenal medulla during development. The cortex finally 

 encloses the medulla completely in mammals (Table 6). 



2.311 Interrenal tissue 



In Elasmobranchii, cortical gland tissue occurs as one or more 

 median yellow masses, the interrenal tissue, so-called from its 

 position between the kidneys. It is widely separated from the paired 



