In the discussion about the relation of parthenogenesis and sex, revived after the discovery of the sex-chromosomes, cases of facultative parthenogenesis in normally bisexual animals play a rather doubtful part. As the great majority of such reports belongs to the older and oldest literature, modern writers appear sceptical in regard to their reliability. Therefore any new case recorded under reliable conditions must command the attention of biologists. The majority of the reports about facultative parthenogenesis relate to the order Lepidoptera. In most cases only the hatching of caterpillars from unfertilized eggs has been observed, which is of no interest for us here. There are comparatively few cases where adults have been raised and their sex stated. One set of observations relates to the silk-moth. This case can be regarded as settled. There can be no doubt to-day that there are races of the silk-moth which exhibit regularly the phenomenon of facultative parthenogenesis and that the normal number of both sexes is produced from parthenogenetic eggs (for example, see Hartmann, '12). Another set of facts relates to the Psychidae, where parthenogenesis is a normal phenomenon, resulting in female offspring. A third series of reports deals with occasional cases of parthenogenesis in the gypsy-moth, Lymantria dispar L. In I870, H. Weijhenberg, Jr., reported that he had succeeded in breeding 27 adults, I4 9 and 13 oP, from 60 virgin females of this moth. He also obtained a second parthenogenetic brood, but he does not give details (see Dohrn, '7I). A second report comes from G. Platner ('88). He claims to have obtained parthenogenetic eggs regularly by keeping the females isolated for a