IN a recent communication1 under this title, Mr. A. C. Evans states that ” Ratcliffe2 has recently suggested that there may possibly be two physiological races of L. sericata, as the length of the pupal period of this insect at 32° C. in Scotland is 5.4 days while in France at the same temperature it is 8 days”. The latter figure was obtained by Ratcliffe (as he states) from an earlier publication of mine3 where I was quoting Cousin4. Evans claims that my quotation is inaccurate and should be 4.9 days, but on further reference to Cousin's work4, I find that it is perfectly correct.