186 HEREDITARY CHARACTERS 



acters in the progeny of the hybrids, have been recorded. 

 There are two series of breeding experiments with silk-worm 

 moths. In the first series, two races of Siamese silk-moths 

 were crossed, in one of which the caterpillar spun yellow, 

 and in the other white cocoons. The result was segregation 

 on Mendelian lines. 1 Another series of experiments with 

 silk-moths gave entirely opposite results. The hybrids were 

 sometimes blends and differed from both parents, sometimes 

 some in the same brood were like one parent and some like 

 the other, and in other cases the individuals of a brood were 

 all like one parent or all like the other. 2 To begin with, 

 it is of course very doubtful whether these silk-moths ought 

 to be taken as natural races. They have been under domes- 

 ticated conditions for hundreds of years in some cases, but 

 the illustration is nevertheless very interesting. It seems 

 probable that in the one case two comparatively newly- 

 established characters were crossed, and that the ancestry 

 of the two races was not at all remote, while in the other 

 the two races had been separated for a much longer 

 period, or even had been derived from two naturally 

 distinct species. 



There are, however, some direct experiments upon un- 

 doubtedly natural races. Individuals of a geometric moth, 

 Acidalia virgularia, from two different races were crossed. 

 The one race, found near London, was dark. The other, 

 from Hyeres in the South of France, was white. Ten genera- 

 tions from this cross were produced, giving between five 

 and six thousand specimens. The results as regards segre- 

 gation were negative. There was great variability and an 

 enormous number of intermediate forms, with apparently 

 a very indefinite tendency to revert. The intergrades be- 

 tween the two parent forms were so gentle that attempts 

 to sort out the specimens into light and dark groups were 



1 Toyama, quoted by J. A. Thomson, Heredity, p. 361. 



2 Coutange, G., " Recherches Experimentales sur I'Her&litd chez les Vers a 

 Sole," Bull. Scientifique de la France et de la Bdgiquc, xxxvii., 1902. 



