Infection with a Single Coccidian Oocyst and Its Significance

their offspring. This character, designated "alae maculatae," proved to be recessive and autosomal. The "alae maculatae" flies had wings darkened along the veins. As this character was found only in one of the F3 cultures it is impossible to say whether the gene calling forth the abnormality was present already in the wild population. No new mutant characters were found in 45 of the F4 and 43 of the F5 crosses. The small scale of the experiment, especially the insufficient number of the F2 cultures raised from each *of the F, crosses (from 3 to 8), probably prevented the detection of all the recessive mutant genes that were present in the initial flies in a heterozygous condition. Nevertheless, the results obtained show positively that the wild population of D. obscura is highly infected with recessive mutant genes, resembling in this respect the populations of D. melanogaster. S. GERSHENSON ZOOLOGICAL INSTITUTE, MOSCOW STATE UNIVERSITY, U.S.S.R.