A cytological survey involving the collection and study of 401 male specimens of two wild populations of grasshoppers belonging to the genusAiolopus was made. In one population, seventeen individuals out of a total of 200 examined had a single supernumerary chromosome in all the dividing cells of their testes, and in the other out of a total of 201 specimens, twenty-nine had one, three had two, and one had three such chromosomes. Moreover, in the latter population two individuals had a varying number of supernumeraries in the different cells of their testes. This difference in the frequencies in the two populations indicates that interbreeding between them is rare or absent altogether. In one of the populations, the frequency of individuals possessing supernumerary chromosomes remained more or less constant between 1947 and 1950. Similar data for the other population have not been obtained. The frequency of individuals with two supernumeraries does not vary significantly from the expected theoretical frequency calculated on the basis of random mating in the population between males and females possessing single such chromosome.