122 CHARLES It. STOCKARD 



the shortest of the eighty-two animals in his generation. 

 There is little doubt that he presents the most pronounced 

 reduction in leg length that can be produced in the basset- 

 hound-Saluki cross. Plate 26 also shows this leg skeleton in 

 company with the F x skeleton and a mixed F 2 to illustrate the 

 increased degree of the achondroplasia reaction in the pres- 

 ence of the genie composition ss as compared with si. 



The leg skeleton to the right in plate 28 shows the chon- 

 drodystrophic reaction of the bulldog constitution to the 

 presence of only a single gene for leg achondroplasia paired 

 with the allelomorph for long. The heterozygous state of 

 this single factor dominant for short achondroplasic legs 

 exerts a considerably greater effect when acting on the bull- 

 dog constitution than does even the homozygous double gene 

 for this dominant expression when acting on the bassethound- 

 Saluki constitution. This fact is vividly shown in plate 28. 

 There is no question that the bassethound-bulldog 1479 5 

 from which the leg skeleton at the right was taken is geneti- 

 cally si. This animal was derived from a backcross between 

 an Fj bassethound-bulldog bitch and a pure bulldog sire and 

 so could only acquire a single s. The leg skeleton from this 

 animal, along with that of its tail, is again shown in plate 

 80 (p. 395) and the animal itself, pictured from life with three 

 other members of his litter, in plate 79 (p. 393). This is indeed 

 a most impressive phenomenon: to observe in the complex 

 mammalian body clearly marked differences in morphologic 

 development due to the presence of only a single or double 

 gene in the genetic constitution. The influence for better or 

 worse of one strange gene in the constitution of higher mam- 

 mals and of man himself gives a thoughtful person adequate 

 reason for concern regarding racial hybridization. In spite 

 of superficial generalities on the part of so-called authorities 

 who claim that all human races are highly mongrelized any- 

 way, available knowledge at present forces us not to accept 

 this statement as correct for manv racial characteristics. 



