Abstract
The effect of temperature on the rate of development of B. orientalis was investigated. Eggs obtained by hormonal stimulation were reared at 9-22.5.degree. C with a variation of .+-. 0.5.degree. C, and development was followed up to the neurula stage. Between 20-22.5.degree. C development proceeded normally with very little variation in time. Large time deviations were evident at temperatures < 18.degree. C, particularly after the commencement of gastrulation. Abnormalities occurred at low temperatures and were common at 9 .degree. C. At 7.degree. C initial cleavage was incomplete and further development did not occur.