In this case, therefore, we have, in the same animal, eggs which can be fertilized and eggs which, without fertilization, develop parthenogenetically, and it is therefore of the greatest possible interest to know the state of matters in them in regard to the directive divisions and the reduction of the chromosomes. Dr. Petrunkewitsch's investigations have shown that in both cases, that is, whether a spermatozoon penetrates into the ovum or does not, a twice-repeated division of the nuclear material in the ovum takes place. Moreover, the two daughter-nuclei which result from the second division do not, as Brauer showed was sometimes the case in _Artemia_, unite again afterwards; they remain separate, and the number of chromosomes--there are sixteen of them--is thereby reduced to half in the segmentation nucleus. But this is not all, for before embryonic development has begun the normal number can be again seen in the segmentation nucleus; the chromosomes must therefore have _doubled their number by division within the nucleus_. It is probable that something similar takes place in the cases of exceptional parthenogenesis which have long been known, but this point has not yet been sufficiently investigated. Nevertheless I cannot pass them over, as they are instructive from another point of view. [Illustration: FIG. 79. The two maturation divisions of the 'drone eggs' (unfertilized eggs) of the Bee, after Petrunkewitsch. _Rsp 1_, the first directive spindle. _k 1_ and _k 2_, the two daughter-nuclei of the same. _Rsp 2_, the second directive spindle. _k 3_ and _k 4_, the two daughter-nuclei. In the next stage _k 2_ and _k 3_ unite to form the primitive sex-nucleus. Highly magnified.]