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 Barthélémy. 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 Barthélémy’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 earlier degrees of development, and dry up. 
Further, Barthélémy 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 Barthélémy’s observa- 
tion that only virgin silkworms from the summer brood produce 
a parthenogenetic brood, and that in the same year; while, on 
1 After von Siebold. 2 Von Siebold, op. cit. 
3 Von Siebold, Beitrdge zur Parthenogenese der Arthropoden, Leipzig, 1871, p. 232. 
