E. V. COWDKY 



tation (Verdozzi). It is not apparent until about forty to fifty days of 

 age (Donaldson). In man, however, it is generally thought (without 

 much evidence) that they are larger in the male. 



Variations form Endocrin Factors. In rats the suprarenals undergo 

 hypertrophy, especially in males, as a result of thyroid feeding (Herring, 



Hoskins(fr)). Carlson has reported, 

 however, that thyroidectomy also causes 

 suprarenal enlargement. Castration 

 causes an increase in the size of the 

 suprarenals in male rats and a decrease 

 in females (Hatai). 



Growth, The growth of the supra- 

 renals is very precocious (Fig. 4), and 

 Jackson (&) has found that it is quite dif- 

 ferent in character from that of the thy- 

 roid and thymus glands. Instead of 

 being gradual and progressive, it is ex- 

 tremely rapid during the third month, 

 when the organs reach their greatest 

 relative size ; from then on they decrease, 

 until in the adult they are reduced to 

 about one one-hundredth of one per cent 

 of body weight. The vigor of their 

 growth energy is shown by the fact that 

 they go on developing and even increase 



slightly in weight in young white rats held at maintenance level of body 

 weight by underfeeding (Jackson (a-)). A differential study of the 

 cortical and medullary portions has very recently been made by Jackson. 



Fig. 4. Dissection of a three 

 months' human fetus showing the 

 relative size of the suprarenal (s) 

 and the kidney (k), after Piersol. 



Comparative Anatomy 



Duality of Suprarenals. Our conception of the dual nature of 

 the suprarenal glands is sustained by our knowledge of their com- 

 parative anatomy. Phylogenetically the cortex and the medulla are en- 

 tirely distinct organ systems and only become topographically associated 

 in the higher forms. The changes are represented in the accompanying 

 diagram. 



Conditions in Various Phyla. In Invertebrates. In invertebrates 

 the medullary portion is represented, perhaps, by certain large cells oc- 

 curring in connection with the abdominal ganglia, which give the chroma- 

 phil reaction, and from which epinephrin may be extracted (Biedl, Gas- 

 kell(c)). Representatives of the cortical substances are, however, un- 

 known. 



In Fishes. Both systems are found in fishes and are quite distinct 



