The Compressibility of Media under Extreme Pressures

With the exception of the Teffe strain which will be dis- cussed in another publication, no trace of sexual isolation is observed between strains of D. willistoni from different parts of Brazil and from Guatemala.When Brazilian males are offered a choice of females of their own and of other Brazilian strains, inseminations occur at random.If a mixture of Brazilian and Guatemalan females are confined either with Brazilian or with Guatemalan males, a greater proportion of Brazilian than of Guatemalan females are inseminated.The mating of Brazilian and Guatemalan flies is, therefore, selective rather than random; however, the particular type of selectivity here observed does not constitute a barrier to gene exchange.1