No. 568] 



BIOLOGY OF THE THY SAN OPT ERA 



247 



be due either to climatic conditions or to racial differ- 

 ences. Sexual reproduction was not wholly proven, but 

 seems probable. An increase in the number of males in 

 late summer in this species and in Thrips tabaci might be 

 interpreted as indicating a sexual phase, or the vestiges 

 of a sexual phase that existed in the species formerly. 

 Jordan's belief in an alternating life cycle, which was 

 rejected by Uzel, thus receives some measure of jus- 

 tification. 



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