37° 



THE PERIPHERAL NERVOUS SYSTEM 



When the cells of the medulla begin to produce an internal secretion they 

 give the chrome reaction. By using extract of the aortic bodies, which are en- 

 tirely composed of chromaffin cells, Biedl and Wiesel have proved that its effect, 

 like that of adrenalin, is to increase the blood pressure. The logical conclusion is 

 that the effect of adrenalin, an extract of the suprarenal glands, is due to an 

 internal secretion produced by the chromaffin cells of the suprarenal medulla. 



sy 



sy sy 





^y 



r 





••N-* 



*i#^:; 



\'?i^ 



b «« 



'K- *.,*.%«;,■■ 'i'*;- 



t ' ■ • . ; 5 V.*.;; 



u»«t: 







Capstile 





■".'4,"' 



^:^^5?'^r 



-sy 





w 



tA 





Fig. 368. — Transverse section through right suprarenal gland of a 15.5 mm. human embryo (after 

 Bryce). sy, Sympathetic cells; sy', groups of chromaffin sympathetic cells migrating into the suprarenal 

 gland. 



Portions of the suprarenal anlage may be separated from the parent gland and form 

 accessory suprarenals. As a rule, such accessory glands are composed only of cortical sub- 

 stance; they may migrate some distance from their original position, accompanjring the 

 genital glands. In fishes the cortex and medulla persist normally as separate organs. 



E. DEVELOPMENT OF THE SENSE ORGANS 



The sense cells of primitive animals (e. g., worms) are ectodermal in origin 



and position. Only those of the vertebrate olfactory organ have retained this 



primitive relation. During phylogeny the cell-bodies of all other such primary 



sensory neurones migrated inward to form the dorsal ganglion (Parker), hence 



