592 



Ontogeny of Endocrine Correlation 



appearance and increase of adrenaline is a 

 peculiar and striking vascular change asso- 

 ciated with the differentiation and migration 

 of the future medullary cells. As shown in 

 Figure 209B, the migrating spherical islands 

 of chromaffin cells in the cortex are provided 

 with a distinctive arrangement of the capil- 



gradually increases, a relationship of a func- 

 tional nature. 



Nothing is definitely known as to the 

 function of adrenaline during fetal life. It 

 is significant to note, however, that almost 

 from the beginning the development of the 

 adrenal medulla and of the sympathetic 



Fig. 211. Section of an adrenal gland showing partial invasion of medullary cells from a mass of sympa- 

 thoblasts (s). Differentiated from an isolate of the mesonephros-gonad- adrenal complex taken from a 4-day 

 chick embryo and grown for 9 days on the chorio-allantoic membrane of a male host embryo, c, Group of 

 cortical cords free of intervening medullary cells; m, medullary cord; w, portion of mesonephros. Initial X 

 200. (From Willier, '30.) 



laries, which, although continuous with 

 those of the cortex, have a smaller meshwork. 

 In both instances the blood is derived from 

 the arterioles in the capsule. As the islands 

 increase in size and move inward toward 

 the central vein the capillary network of 

 each of them is provided with a separate 

 arteriole. For a short time the capillaries of 

 the cortex act as venules from the capillaries 

 of the island (Flint, '00). These changes in 

 vascular pattern are of a kind that permit a 

 more efficient flow of blood to the islands of 

 chromaffin cells. Apparently as the mode of 

 blood transportation becomes more efficient 

 the adrenaline content of the adrenal gland 



nervous system is interlocked. In the course 

 of their functional development the former 

 becomes in effect an integral part of the 

 latter (constituting the so-called "sympatho- 

 adrenal system"). It would be of much sig- 

 nificance to determine at the time of first 

 appearance of adrenaline, as well as during 

 its increase in the fetal adrenal, whether 

 splanchnic nerve fibers (preganglionic) al- 

 ready terminate around the individual 

 chromaffin cells, as they do in the adult. 

 The possibility, however, that the chromaffin 

 cells may form and store adrenaline as 

 chromophile granules before innervation is 

 established must be recognized, since these 



