46 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



the other hand, no offspring was hatched from parthenogenetic 

 eggs of either the summer or autumn brood when kept over 

 winter. Von Siebold brings forward observations by himself 

 and Schmid which confirm Barthelemy's latter contention, at 

 least in part. 



These investigations on silkworms are of especial interest 

 to us, because we are here concerned with a transition form in 

 the sense that the eggs of the silkworm show a tendency toward 

 spontaneous parthenogenesis; but it depends upon certain as 

 yet unknown conditions whether or not the eggs develop spon- 

 taneously, i.e., without fertilization, and whether development 

 stops in the initial stages, or whether the complete development 

 to caterpillar or imago takes place. This is supported by the 

 fact that different authors have achieved such contradictory 

 results. It is possible that not only external circumstances, 

 but also conditions which belong to the egg itself (e.g., the 

 nature of the shell) here come into play. We shall meet later 

 a similar case in the parthenogenesis of starfish eggs. 



Von Siebold, Leuckart, and other authors have extended the 

 observations on natural parthenogenesis with reference to the 

 importance which these observations possess for another funda- 

 mental problem of biology the determination of sex. In the 

 Psychidae and in Solenobia the parthenogenetic eggs give rise 

 only to females, in bees only to males. Leuckart and von 

 Siebold discovered that in other hymenoptera too (Polistes, 

 Vespa, and Nematus) similar things take place, and that here 

 too parthenogenesis occurs, leading, however, exclusively to 

 the production of males. In Crustacea, such as Apus, Artemia, 

 and Luimadia, von Siebold likewise found parthenogenetic 

 development ; but here it led to the production of females only. 



This sketch of the earlier observations upon spontaneous 

 parthenogenesis will suffice for the comprehension of the ex- 

 periments on artificial parthenogenesis with which they are 

 historically connected. 



