A CASE OF FACULTATIVE PARTHENOGENESIS. 39 



by the x-chromosomes and following their distribution. The 

 possibilities are now as follows: 



1. Female heterozygosis. 9 = (FF) Mm, & = (FF) MM. 



A. Parthenogenesis occurs with the reduced number of 

 chromosomes. Offspring must be female as no set MM 

 can be produced. 



B. Parthenogenesis occurs with normal number of chro- 

 mosomes in consequence of no reduction-division taking 

 place. All offspring are female, as the maternal com- 

 bination is preserved. 



C. Parthenogenesis occurs with the normal number of 

 chromosomes, reached by readjustment after reduction. 



a. Readjustment accomplished by conjugation of egg 

 and polar nucleus. All offspring female, since 

 maternal combination remains. 



b. Readjustment accomplished through rudimentary 

 division before cleavage. The reduction had led to 

 eggs with M and eggs with m. M eggs then become 

 MM, i. e., males, m eggs become mm, i. e., females, 

 if viable at all. 



Conclusion. Parthenogenesis with female heterozygosis can 

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

 Co); (b) males exclusively (case Cb when mm eggs not viable); 

 (;) both sexes (case Cb if all eggs are viable, or any combination 

 of Cb with the other cases). 



2. Male heterozygosis. (MM) FF -- 9 ; (MM) Ff = = cf. 



A. Parthenogenesis occurs with the reduced number of 

 chromosomes. Offspring nothing but males. However, 

 the occasional formation of females is possible when a 

 case of non-disjunction occurs, leaving both FF inside 

 the egg. 



B. Parthenogenesis occurs with the normal number of chro- 

 mosomes in consequence of the failure of reduction. The 

 maternal combination being preserved, all offspring are 

 female. In this instance males can be produced if one 

 x-chromosome is extruded during the equation division. 



C. Parthenogenesis occurs with the normal number of chro- 

 mosomes reached by readjustment after reduction. 



