238 Isabel McCracken 



CONCLUSION 



The characters S, B and AB in this species are mutually exclu- 

 sive. The conditions of dominance and recessiveness are relative 

 conditions. B is recessive to S, dominant over AB. It is latent 

 in AB as a sport. S is dominant over both B and AB. AB is 

 recessive to both S and B. It may contain latent B, but appar- 

 ently does not contain latent S. AB as a sport is a stable character, 

 not at first absolutely so, but by selection becoming quite as much 

 so as either S or B. 



That there is no apparent tendency toward trichromatism tak- 

 ing the place of dichromatism in the species, seems to be due to 

 the as yet very small proportion of AB individuals normally pro- 

 duced, the remote chance of an AB type meeting with a mate of 

 similar type and the swamping effect of back-crossing. 



In this species, therefore, it seems, as suggested by Darwin in 

 1859,^ that owing to the "nature of the organism," each type 

 would ultimately become a fixed type if the "nature of the con- 

 ditions" favored it. The "nature of the organism" — that is, the 

 origin of somatic variations having hereditary value, the relation 

 of these in the germ-cell elements or the inherent quality that 

 makes for dominance or prepotency and the quality that makes 

 for purity — this is the obscure point. 



^Darwin: Origin of Species, p. 77. 



EXPLANATION OF PLATE 



Fig. I Melasoma scripta (Fabr.) type with spotted elytra. (S) 



Fig. 2 Melasoma scripta (Fabr.) type with black elytra. (B) 



Fig. 3 Melasoma scripta (Fabr.) all black sport of occasional occurrence. (AB) 



Fig. 4. Melasoma scripta (Fabr.), mosaic type of 2 and 3 resulting from intermating or back cross- 

 ing 3- 



