SUMMARYEffective measurement of sternite size, as a means of evaluating abdominal size, is made possible by the use of a microscope with a stretching apparatus.On this basis, the difference between abdominal size in two colonies of the same race was found to be not significant. On the other hand the differences between sternite measurements in the twoApisspecies were highly significant.It was found that the length and width of sternites 4, 5 and 6 are more closely correlated with abdominal size than are the length and width of sternites 3 and 7. Sternite 6 is comparatively short and wide, and its length and width can be measured easily and accurately on one microscopic field graduated in the same unit; this is not true for sternites 4 and 5, which are therefore less useful.