The Determination of Sex 373 



of the eggs (those that formerly produced males, let us say) 

 are present and fail to develop. The alternative view seems 

 more plausible, that all the eggs produce females. If this view 

 is the correct one, then we find that in parthenogenetic species 

 two changes have occurred, all the eggs produce females, and 

 at the same time these female eggs have acquired the power to 

 develop without fertilization. It may be that both processes 

 have gone on hand in hand, and the same tendency to develop 

 parthenogenetically is associated with a tendency to produce 

 only females. In not a single case has the sex of the embryo, 

 produced by artificial means, been determined, therefore we 

 lack experimental evidence to form any opinion on this point. 

 In species where occasional parthenogenesis occurs both male 

 and female individuals may develop from unfertihzed eggs, as 

 in the silkworm moth. In other groups apparently more females 

 develop, as in certain other moths, but in these the process of 

 parthenogenesis is sometimes quite regular rather than occa- 

 sional. In the honey bee and in some other hymenoptera, 

 males as a rule develop from parthenogenetic eggs. 



Whatever conclusion we reach finally in regard to the origin 

 of parthenogenetic species, one point must be always borne in 

 mind : parthenogenetic eggs carry latent, or in a potential con- 

 dition, the male characters which may at any time become domi- 

 nant. There are certain species that produce only partheno- 

 genetic females in one generation, but males and females in 

 approximately equal numbers may appear in the next generation, 

 as in the gallflies ; and in other species that have a long succes- 

 sion of parthenogenetic females, males and sexual females may 

 appear in at least equal numbers. These cases seem to indicate 

 with some probabihty that parthenogenesis has not arisen by the 

 suppression of the male eggs, but by the dominance of the female 

 characters in all of the eggs. What is true for the so-called female 

 eggs is probably also true for the male-producing eggs in uni- 

 sexual forms. The male egg carries latent the characters of 

 the female, and the hereditary transmission by means of the male 

 of the maternal characters shows that this must be the true view. 



