40 RICHARD GOLDSCHMIDT. 



a. Readjustment through conjugation of egg and polar 

 nucleus. The maternal combination being pre- 

 served, only females are produced. 



b. Readjustment through rudimentary division before 

 cleavage. Only female offspring result, since every 

 egg contains FF. In case of non-disjunction, an ex- 

 ceptional male may appear, provided an ff egg is 

 viable. 



Conclusion. Parthenogenesis with male heterozygosis can 

 result in the production of (a) females exclusively (cases B, C), 

 exceptional males explained by Cb or the occasional occurrence of 

 A or B; (&) males exclusively (case A}, exceptional females ex- 

 plained by Ron-disjunction or the occasional occurrence of B, C; 

 (c) both sexes (case B or combination of A with B or C). 



We may now, by surveying briefly the facts known about par- 

 thenogenesis, show that the above explanation holds good for 

 all of them. 



i. Hynienoptera. The classic case of the bee is of special 

 interest because it demonstrates the possibility of sex-differen- 

 tiation without the use of the usual method of the formation of 

 two kinds of gametes. It is important also because it shows 

 that we are entirely at a loss if we express ourselves in Mendelian 

 symbols without referring to the cytological facts. Partheno- 

 genetic eggs produce males which develop with the reduced 

 number of chromosomes. 1 We are concerned with case 2A of 

 the series above described. In spermatogenesis no reduction 

 occurs and only one kind of spermatozoa is formed, being in con- 

 stitution identical with the ripe egg. Every fertilized egg, 

 therefore, develops into a female. Occasional females derived 

 from parthenogenetic eggs reported from time to time (the 

 same for ants) can be explained by non-disjunction (2 A) or 

 the occasional occurrence of 2B, C. Occasional males from fer- 

 fertilized eggs are also possible if a non-disjunction egg (with 

 both FF in the polar body) is fertilized. 



The other hymenoptera show no difference in principle. 

 Where parthenogenesis results in the formation of both males and 

 females, the former develop with the haploid number of chro- 



1 For cytological facts see Nachtsheim, H. ('13). 



