ENDOCRINAL SYSTEM 569 



Elasmobranchs correspond to the medullary part in 

 Mammals, while the interrenals of Elasmobranchs and 

 the suprarenals of Teleosts and Ganoids correspond to 

 the cortical portion in Mammals. The function of this 

 cortical portion is quite obscure but certainly important, 

 since operative removal of this portion is soon fatal ; there 

 is no evidence that any hormone is secreted in this region. 

 The hormone secreted by the medullary portion, on the 

 other hand, is well known as adrenalin or adrenin, and has 

 been prepared synthetically. It has a remarkable action 

 upon the parts innervated by the sympathetic system 

 (with the exception of the sweat glands), producing on 

 injection the same effects as stimulation of the sympathetic 

 would have, e.g. constriction of the arterioles with conse- 

 quent heightening of the blood pressure, increased strength 

 of the heart-beat and rate of pulse, mobilisation of the 

 store of glycogen in the liver, contraction of the smooth 

 muscles of the skin, etc. It is considered that adrenalin 

 is secreted, under nervous control, in emergencies, and 

 serves to prepare the body for violent efforts. In Reptiles 

 and possibly in lower groups adrenalin probably plays a 

 part in controlling the contraction and expansion of the 

 pigment cells (melanophores) of the skin. There is some 

 indecisive evidence that adrenalin occurs in Annelids. 



Pituitary body. — This little organ is also complex, both 

 morphologically and physiologically. The anterior part 

 is formed from a pouch pinched off from the roof of the 

 stomodaeum, and is glandular in structure. It forms an 

 imperfectly known internal secretion which controls 

 growth ; overgrowth or excessive activity of these regions 

 leads to giantism, or at least an enlargement of the bones 

 and fleshy parts of the face and extremities, which is 

 known as acromegaly. The posterior part develops from a 

 down-growing nervous tissue from the thalamencephalon, 

 invested by an intermediate layer of stomodaeal origin ; this 

 region appears to be the source of at least three different in- 

 ternal secretions (Dale). One of these causes a rise of blood 

 pressure in Mammals, but not in Birds, by contraction of 

 the arterioles and especially of the capillaries ; another, 

 active even in enormous dilution (one part in a hundred 

 thousand millions), causes powerful contractions of smooth 



