A CASE OF FACULTATIVE PARTHENOGENESIS. 37 



Fi-hybrid between a European and a northern Japanese race of 

 gypsy. But neither the parental races nor the other FI and F 2 

 individuals produced parthenogenetic eggs, although ample 

 opportunity was given to man)' isolated females. This fact 

 neither excludes nor favors the possibility of parthenogenetic 

 strains or mutations. 



In order to give an interpretation of these facts it is \ery im- 

 portant to knovV the beha\ior of the chromosomes of these par- 

 thenogenetic eggs. A study of the maturation divisions was, 

 of course, impossible. But we were able to ascertain that ovo- 

 gonia, as well as spermatogonia, of the parthenogenetic cater- 

 pillars contained the normal (diploid) number of chromosomes. 

 A visible difference between the chromosome-sets of the two sexes 

 does not, however, exist in the gypsy-moth. The literature on 

 parthenogenesis contains, so far as we are aware, only two state- 

 ments which relate to our case. One is Platner's already quoted 

 paper, where he states that the reduction-divisions in parthe- 

 nogenetic dispar-eggs are normal. However, he does not men- 

 tion the chromosome numbers and we do not know whether the 

 eggs studied by him would have developed. Henking ('92) 

 studied the reduction-divisions of parthenogenetic silk-worm 

 eggs and found a normal reduction-division. But his eggs never 

 developed embryos; therefore his results are of no value for us. 



For a real understanding of the relation of parthenogenesis to 

 sex it is very important to know how the diploid number in other 

 parthenogenetic animals is formed. If we compare our case 

 with others where the cytology of parthenogenesis has been 

 worked out, we immediately realize that there are different pos- 

 sibilities. In the first place, parthenogenesis could occur without 

 a reduction-division, as seen in aphids and other forms. Or 

 parthenogenesis could be started after a reduction-division by 

 secondary fusion of the egg-nucleus and the reduction-nucleus, 

 as has been shown for Artemia and the starfish. Or, thirdly, an 

 apparently normal formation of the polar bodies could occur, but 

 without reduction of the chromosomes, caused by their failure 

 to conjugate, as has been shown for Nematus (Doncaster, 1906) 

 and Rhodites (Schleip, 1909). Finally, it is possible that, after 

 normal reduction-divisions, the diploid number is restored before 



