2IO HEREDITY AND EUGENICS 



cent, or more for some characters to 50 per cent, 

 or more for others. Laughhn's scheme is based upon 

 the known constitution of the germ plasm — i.e., its 

 division into chromosomes, each bearing its group of 

 genes ; and ancestral influence is measured by tracing 

 individual chromosomes backwards through previous 

 generations. The " trail " of a given chromosome 

 in the ascendant or descendant generations will depend 

 upon the laws of probability and recombination, and 

 these laws will differ for the ordinary chromosomes 

 and the X and Y chromosomes. On this basis various 

 mathematical formulae are developed for calculating 

 ancestral influence. 



The Basis of Racial and Temperamental 



Differences. 



In discussing questions of elimination or increase 

 of certain types or characters, it is very desirable to 

 know not only what relation these characters bear 

 to the economy of the organism, but also what are 

 their sources and controls in its development. The 

 ductless or endocrine glands, which have been studied 

 in recent 3^ears, are of the utmost importance in this 

 connection. The}' pour direct h' into the blood in 

 minute quantities hormones which influence and con- 

 trol directly the activities of various organs of the 

 body. They also form a system of checks and 

 counterchecks to each other, and so constitute a 

 sort of interlocking directorate, exercising the most 

 complete control over the bodily activities, as a whole, 

 through the medium of the substances they discharge 

 in minute traces into the blood. These glands have 

 a very long evolutionary history, being derived 

 from totalh^ different organs having other functions, 

 which are present in the lower vertebrates (Chordates) 

 such as Amphioxus . 



In his presidential address to the Anthropological 



