SOMATIC MUTATIONS OF BRUCHUS. 15 



This proves that white was not transmitted to any offspring; on 

 the other hand, no tan-white insects have so far appeared. 



Another kind of mosaic that was found frequently among the 

 offspring from the wild cultures was an animal with one black 

 elytrum. Six (Mosaics 3, 14, 16, 18, 20, and 30) of these females 

 had tan, left elytra and black, right ones, while one (Mosaic 6) had 

 a black, left elytrum and a tan, right one. 



To illustrate the tan-black type, Mosaic 14 will be described. A 

 mosaic female was observed after she had emerged with many 

 other insects from a wild culture on January 5, 1919. This female 

 had a normal, tan body and tan, left elytrum, while her right 

 elytrum was black. When mated with a normal (tan) wild male, 

 her offspring produced through three generations 511 tan or wild 

 descendants. This type of a mosaic proves that black was not 

 transmitted, because it did not appear in any offspring ; again black 

 appeared in this insect because black is a dominant to tan, its reces- 

 sive allelomorph. 



Of the black-tan, Mosaic 6 is the only one which was observed. 

 She was found in a culture from wild parents on September 30, 

 1918. Her body and right elytrum were both tan, but her left 

 elytrum was black. She was mated to a wild male and produced 

 339 homozygous, wild progeny. The result shows that the black 

 visible in this mosaic was not transmitted because it is a somatic 

 dominant to tan (the wild type). 



DISCUSSION. 



The result of the experiments previously described shows that 

 these somatic modifications in Bruchus, which concern the elytra 

 of the females, are not clue to factor mutations in the germ cells, 

 because they are not transmitted. It seems, therefore, that the best 

 interpretation is to assume that they are somatic mutations. Ordi- 

 nary somatic variations are modifications that are supposed to be 

 caused by environmental factors, as they are not inherited. They 

 always display a normal variability curve. The converse of this is 

 true, for these mosaics, since they manifest a sharp discontinuous 

 variation, not unlike a mutation. Mutations have usually been de- 

 scribed as discontinuous variations that breed true. A mutation 

 that occurred in a germ cell in an animal would breed true because 



