3IO 



WILLIAM LAWRENCE TOWER. 



signaticollis type. 



mid. type. 



undecimlineata type. 



2,452 



827 



218 



showing again a marked decrease in the undecimlineata form, a 

 lesser decrease in the intermediate hybrid type, and a much 

 greater relative increase in the signaticollis type. These hiber- 

 nated during the winter of 1905-1906 and emerged in June, 1906. 

 They were allowed to interbreed freely. The population was 

 not seen at the time of emergence, but in the fourth generation 

 it was observed in July, 1906, and the 11-lineata type and the 

 mid type were nearly absent. The census made at this time, 

 when the first generation of the year was apparently at its height, 

 gave the following results: 



These then inbred and the colony was next seen in September 

 at about the middle of the month, when the census of the indi- 

 viduals in the colony was as follows in Generation V. : 



These hibernated during the winter of 1906-07 and emerged in 

 June, 1907, reproduced at once, and gave an abundant progeny 

 which emerged as Generation VI. between the loth and 25 th of 

 July. These when seriated gave the following results: 



The second generation of 1907 emerged late in August and 

 early in September, and of this generation the undecimlineata type 

 was entirely absent, and the mid type practically so. These hiber- 

 nated and when seen in the spring of 1908 only the signaticollis 

 type emerged. Both generations of 1908 and both generations 

 of 1909 have developed the presence of the signaticollis type 

 only. 



