GENES IN RELATED SPECIES 99 



with mutant characters, seven in all. The mutant charac- 

 ters were inherited in the same way as in C. porcellus. 

 This result again shows that the two species carry some 

 identical loci. The results do not show, however, that 

 identical mutants exist in the two species, for no mutant 

 races with characters similar to those of porcellus have 

 been studied. 



a 



c d 



Ftg. 57. 

 a, Helix nemoralis, 00000, yellow, Zurich type; b, ditto 00345, red- 

 dish (Aarburger type); c, typical H. hortensis, 12345; d, ditto; 

 e, hybrid 00000. (After LaDg.) 



One of the clearest cases where the characters of one 

 species behave toward the characters of the other species 

 in the dominance-recessive relation as do the same 

 character-pairs within the species is described by Lang 

 in his experiments with two wild species of snail, Helix 

 hortensis and H. nemoralis (Fig. 57). 



There are two wild species of Drosophila that are so 

 much alike externally that they were put into the same 

 species. One is now called D. melanogaster, the other D. 



