The cytology of two species of Luffia has been studied. The first one, L. lapidella, is bisexual, the second one, L. ferchaultella, parthenogenetic and derived from the first. In both species the females have a diploid number of 61 chromosomes. The male of lapidella has 62 chromosomes. The development of the fertilized egg of L. lapidella does not show any noticeable peculiarity other than the slow rate of the first meiotic division. The meiotic divisions of the parthenogenetic egg of L. ferchaultella begin normally as in lapidella but are interrupted either at the end of anaphase I or at metaphase II or anywhere between these two stages. Through various procedures the two haploid plates reunite to form a new metaphase spindle, which carries out a normal though diploid second meiotic division. The restoration of the diploid number happens therefore by means of the fusion of the first polar body with the nucleus of the oocyte II. The different procedures which lead to it have been studied and their variability examined in connection with the environment, the morphological types of the females and the geographical distribution of the species.