From a preliminary study of the factors accompanying and influencing metabolism as determined by the 0 consumption during embryonic development made on Anasa tristis De G., Tropaea luna L., Samia cecropia L., and Pyrausta ainslei Hein., the following conclusions are drawn The weight of the egg shell is an important factor and should be taken into consideration. The effects of temp. are not so pronounced during the formative period as during the period of late incubation. The explanation offered for the variation in the length of the formative period is the length of the incubation period and not the place where the eggs chance to be laid, as has been suggested.