Natural Parthenogenesis 45 



and by others in addition have led to remarkable results. 

 Herold had already observed in 1838 that a certain percentage 

 of the unfertilized eggs of the silkworm begin to develop, but 

 that, in contradistinction to the fertilized eggs, the development 

 of the unfertilized ones comes to a halt in the first stages, and 

 that such parthenogenetic eggs never succeed in forming cater- 

 pillars-.' Schmid and von Siebold^ observed the hatching of 

 caterpillars from unfertilized eggs of Bombyx mori, and these 

 caterpillars developed into sexually mature animals. But 

 the results of other observers remained in part contradictory. 

 All found that the first developmental stages occurred also 

 in the unfertilized eggs, but in the majority of cases the eggs died 

 during the winter. In the year 1871 von Siebold returned^ 

 to the question of parthenogenesis in Bombyx mori once more, 

 and mentioned the investigations of Barth^l^my. This author 

 found that development starts very much later in the unferti- 

 lized eggs of Bombyx mori than in the fertilized ones. 



The number of the unfertilized eggs, in which the actual hatching 

 of the caterpillar through parthenogenetic development was reached, 

 was also extraordinarily variable; only once in Barthdl^my's investi- 

 gations did it happen that nearly all the unfertilized eggs of a virgin 

 silkworm developed, while those cases in which all the unfertilized eggs 

 laid by Bombyx mori remained sterile were very abundant. For in 

 cases where development does take place among the eggs laid by a 

 female silkworm, only three or four eggs at most accomplish the last 

 stage of development, i.e., the hatching of a caterpillar; the rest remain 

 at various earUer degrees of development, and dry up. 



Further, Barth^lemy remarks that these strains bred from 

 virgin silkworms proved just as strong as those produced under 

 the influence of the male silkworm; moreover, these individuals 

 sprung from virgin silkworms showed perfectly normal sexual 

 instincts. Of the highest importance is Barthelemy's observa- 

 tion that only virgin silkworms from the summer brood produce 

 a parthenogenetic brood, and that in the same year; while, on 



' After von Siebold. ' Von Siebold, op. cit. 



' Von Siebold, BeitrUge zur Parthenogenese der Arthropoden, Leipzig, 1871, p. 232. 



