1917 ENTOMOLOGICAL SOCIETY. 67 



organs were developed to a certain stage, to unusual coiidiiions of temperature ajid 

 moisture. As a result variations appeared in the offspring in regard to color 

 markings and certain details of structure. These variations, moreover, were not 

 all alike; some were immediate, others appeared after a time; some of the germ 

 cells were affected, others were not. But the important point was that the varia- 

 tions produced did not revert to the original parent forms in subsequent genera- 

 tions. These experiments indicated that environmental stimuli fiiaij, under certain 

 conditions, produce {jerminal variations. 



Standfuss and Fischer, by changing the temperature and food of the larva 

 of Vanessa and Arctia, induced in the following generations certain variations 

 which persisted even when crossed with the parent form. 



The investigations of Johannsen, of Copenhagen, with Pure Lines of beans 

 and barley showed that variations within a Pure Line arc not inherited, and that 

 they have little or no influence on the permanent improvement of a race. In 

 Tower's experiments with Pure Lines of the Colorado Potato Beetle (Leptinotarsa 

 10-lineata) dark to light colored variations appeared in the same Pure Line. 

 When dark males and females w^ere mated the progeny were not dark, but they 

 fluctuated about the average of the Pure Line, even after twelve generations of 

 such mating. Towers results, therefore, confirm the conclusions reached hy 

 Johannsen. 



Selection Value of Vakiations. 



Darwinism has been criticized on the ground that variations often occur 

 which cannot possibly be of value to their possessors in the struggle for existence. 

 Kellogg and Bell in their " Studies of Variation in Insects " made a careful 

 scrutiny of the color patterns of 1,000 specimens of Hippodamia convergens and 

 found 81 aberrations of pattern varieties, ranging all the way from no spots to 

 eighteen spots, although twelve is the species character. If some of the inter- 

 mediate patterns should disappear the systematist would have data for making 

 several new species. Other forms studied showed variations in antennal structure, 

 spinal armature of tibia}, and venation. The conclusion is that " continuous " 

 variations are in all probability not the foundation stones of new species. This 

 view has of course been emphasized by De Vries, Johannsen, Morgan and others. 



Examples of Mendelism. 



Toyama's experiments with Siamese silk moths are interesting. He paired a 

 moth with yellow cocoons with one liaving white cocoons. The offspring produced 

 only yellow cocoons. In the next generation some of the cocoons were yellow and 

 some were white in the proportion of 3 to 1. The whites bred true, while the 

 yellows broke up again, yellows and whites in the usual ratio. 



Miss McCracken's work with spotted and black varieties of TAna lapponica is 

 also confirmative of Mendel's laws, the spots being dominant and the black 

 recessive. 



Coutagne, 1902, found that when a silk moth whose larv.ne had transverse 

 stripes was crossed with one whose larva3 were white, the striped form was dom- 

 inant. Toyama also found the striped form dominant. 



Standfuss's experiments in crossing the moth AfjlUi tau with its dark variety 

 h^'jens do not harmonize with those of Doncaster with Abraxas. The dark color 

 of higens was dominant over the light color of tau. but in subsequent matings of 

 heterozygous lugcns and with tan the results were such that cannot be brought into 

 line with Abraxas. 



