406 CHARLES R. STOCKARD AND E. M. VICARI 



gram of body weight, the largest proportion being more than 

 twice the smallest. The relative sizes of the thyroid in the 

 bassethound show less than half the range in variability 

 shown for the bulldog. 



Text-figure Si gives the relative sizes of the thyroid for 

 the great Dane and St. Bernard, two giant breeds of dogs. 

 The series of bars at the left represents two male and four 

 female great Danes. The relative amounts of thyroid in 

 these large animals, each weighing about 50 kilograms, are 

 uniformly small, ranging from 80 to 130 milligrams per kilo- 

 gram of body weight. The largest is only 14 times greater 

 than the smallest, a much lower variation in size than is 

 shown for the two dwarf and the two normal sized breeds 

 discussed above. 



The next series of bars in text-figure 81 represents the rela- 

 tive thyroid sizes for ten adult St. Bernard dogs, two males 

 and eight females. Several of these dogs weighed close to 

 100 kilograms and showed marked symptoms of acromegaly. 

 The relative amounts of thyroid tissue are comparatively 

 very low, being smaller than for any of the above five breeds. 

 The range is from 45 milligrams per kilogram up to 125 

 milligrams, the upper extreme being almost three times the 

 lower, with an average for the ten animals of only 85 milli- 

 grams. 



These fairly representative groups of six pedigreed dog- 

 breeds of highly different types clearly indicate w T ide ranges 

 of variability in the relative amounts of thyroid tissue pos- 

 sessed by closely similar specimens within each group. The 

 greatest range of variability in relative thyroid size is among 

 the. English bulldogs. These may be said to differ more widely 

 from the ancestral canine pattern than do any of the other 

 five breeds discussed. Yet in spite of their extremely modified 

 type, there is no evidence that the wide differences in pro- 

 portional amounts of thyroid material are at all concerned 

 with the degrees of development in their structural distortions. 



The smallest range of variability in thyroid size is shown 

 by the Great Danes. These dogs are of giant size, but of 



