GENETIC TYPE AND THE ENDOCRINES 9 



recorded, as well as studies of the modifications in instinctive 

 behavior and psychologic reactions. The expression of in- 

 stinctive and conditioned reactions as definite hereditary 

 entities has also been investigated. 



Varieties of form among the dog breeds. No other species of 

 mammals presents such wide diversities in structural type and 

 general behavior as are shown among the breeds of domestic 

 dogs. More than 100 separate breeds now exist. The exhibits 

 in kennel shows in America and the European countries bring 

 together most remarkable examples of structural deviations 

 from a wild or ancestral dog type. These deviations involve, 

 in the first place, the size of the individual, as illustrated by 

 the tiny midget Chihuahua of less than 1 kilogram adult 

 weight, as well as the Pomeranians, sleeve Pekingese, midget 

 pinchers and others almost equally tiny. Such toy breeds 

 are contrasted with the gigantic great Danes, St. Bernards 

 and Irish wolfhounds, the largest specimens of which weigh 

 nearly 100 kilograms. In other words, adult dogs at opposite 

 ends of the size scale differ in weight by 100 times. Equally 

 striking contrasts are seen in head shapes, from the round 

 head with flat muzzle of the Brussels griffon, the pug and the 

 bulldog, to the long, slender muzzle and head of the ancient 

 Saluki and greyhounds. Body shapes and proportions range 

 from short, stocky and rounded to long and tapering and, 

 further, to a peculiarly emaciated thinness. The legs are 

 extremely long in the wolfhound, long and very slender in 

 the greyhound, and long and strong in the great Dane and 

 shepherd dogs, while they are short and strong in other 

 hounds, still shorter but straight and stocky in the bulldogs 

 and finally extremely short, bent and twisted in posture in 

 the dachshund, bassethound, Pekingese and others. In the 

 latter breeds, the long bodies may actually at times drag on 

 the ground. Tails also differ greatly among dog breeds, from 

 the long, slender and straight tails of the pointers, setters 

 and foxhounds, to the heavy, short and curled tails of the 

 huskies, chows and Pomeranians, still further to the even 



