Hormones and Heredity 173 



sweetbread. It excites this gland to secrete its very 

 important digestive juice, which is poured into the 

 food-canal. Thus, when a meal is in process, or it 

 may be in pleasant prospect, there is by means of the 

 hormone secretion a preparation for its digestion. 

 This illustrates what is meant by physiological co- 

 ordination or correlation, for it is plain that the 

 beginning of the intestine and the pancreas work 

 into one another's hands. 



Of great interest are the hormones which pass from 

 the reproductive organs throughout the body and 

 awaken adolescent changes in many parts. The male 

 frog's swollen first finger, the nuptial adornments of 

 many cock-birds, the antlers of the stag, may be 

 mentioned as familiar masculine features which are 

 activated by the reproductive hormones. In many 

 cases the female organism has the masculine char- 

 acters lying latent, inhibited by chalones from the 

 ovary. Thus we understand why a duck from which 

 the ovary has been removed should put on the precise 

 livery of the drake, and assume some of his ways as 

 well. Not less important are the hormones which pre- 

 pare the mammalian mother for the gestation and 

 nurture of the offspring, and an interesting light is 

 shed on the intimacy of the ante-natal partnership or 

 symbiosis by the discovery that there is not only a 

 passage of hormones from the mother to the unborn 

 offspring, but a passage of useful hormones from the 

 offspring to the mother. It is probable that there are 

 hormones to be discovered in plants, and their dis- 

 covery among backboneless animals has begun, but 



