MODES OF EVOLUTION 



251 



Fic. 120. 



secretions of the pituitary are abnormally active (hyperpitui- 

 tarism) the hand becomes broad and the fingers stumpy (Fig. 

 118, B). If the secretions of the pituitary are abnormally re- 

 duced (hypopituitarism) the fingers become tapering and slender 

 (Fig. 118, C). Thus in a most remarkable manner the internal 

 secretions of a very ancient 

 ductless gland, attached to the 

 brain and originating in the 

 roof of the mouth in our most 

 remote fish-like ancestors, affect 

 the proportions both of flesh 

 and bones in the fingers, as 

 well as the proportions of many 

 other parts of the body. 



Whether this is a mere co- 

 incidence of a heredity-chro- 

 matin congenital character 

 with a mere bodily chemical 

 messenger character it would 

 be premature to say. It cer- 

 tainly appears that chemical in- 

 teractions from the pituitary body control the normal and ab- 

 normal development of proportions in distant parts of the body. 



Chief Modes of Evolution of Mammalian Characters 



What we have gained during the past century is positive 

 knowledge of the cliiej modes of evolution; we know almost the 

 entire history of the transformation of many different kinds of 

 mammals. 



These modes as distinguished from the unknown causes are 

 expressed in the following general laws: first, the law of con- 

 tinuity; Natura non facit saltum, there is prevailing continuity 



Result of Removing the 

 Pituitary Body. 



twelve months 



(Right.) Normal do, 

 old. 



(Left.) A dog of the same age and litter 

 from which the pituitary body was 

 removed at the age of two months. 



After Aschner. 



