410 CHARLES Ft. STOCKARD AND E. M. VICARI 



although they are somewhat larger in body size than either 

 parent. 



The next scries of bars in text-figure 79 represents the 

 relative sizes of thyroids for thirty-three P 2 hybrids. These 

 sizes range from a mere 60 milligrams per kilogram of body 

 weight up to the enormous proportion of almost 750 milli- 

 grams per kilogram. The highest amount of thyroid is thus 

 more than twelve times greater than the smallest. These F 2 

 Boston terrier-dachshund hybrids also exhibit remarkable 

 contrasts in type and in the recombinations of characters 

 derived from the two parent stocks. This has been discussed 

 in previous chapters and is well illustrated in plate 30 (p. 129). 

 The contrasts in characteristics among members of the F 2 

 generation supply most valuable test material for determin- 

 ing the possible correlation between relative amounts of 

 thyroid tissue and modified physical peculiarities. Taking into 

 consideration the two most striking character differences 

 among these F 2 hybrids — leg form, long-straight or short-bent ; 

 and head type, long muzzled dachshund form or short-wide 

 Boston terrier shape — we find no relation whatever between 

 the distribution of these different characters and the regularity 

 of the slope formed by the bars representing relative thyroid 

 sizes. Short-bent legs and long-straight legs occur in animals 

 represented for relative thyroid sizes by adjacent bars 

 throughout the series. Head shapes of Boston terrier pattern 

 and dachshund pattern are also irregularly distributed among 

 the individuals from one end to the other of the series for 

 thyroid sizes. The animal with the smallest amount of thyroid 

 has a Boston terrier typed head, while the next highest thyroid 

 record is derived from an individual with a dachshund-like 

 head. The two extremely large thyroid sizes in the F 2 series 

 are recorded from litter mate sisters. One of these showed 

 the mixed combination of short-bent dachshund legs and a 

 Boston terrier typed head, while the other had long, straight 

 Boston terrier legs and a dachshund-like head. These pro- 

 portionally huge thyroids seemed to fit equally well into both 

 si rnctural complexes. 



