V 
SOME EARLIER OBSERVATIONS ON NATURAL PAR- 
THENOGENESIS IN INSECTS 
Long before the importance of the spermatozocn in fertili- 
zation was fully recognized, Réaumur, Bonnet, and a number 
of other eighteenth-century authors had established the fact 
that plant lice bring forth living young without previously 
pairing. Kirby! found that under ordinary conditions of tem- 
perature and moisture, the parthenogenetic generations of 
aphides can follow one another for four years (possibly in- 
definitely) without as a rule giving rise to males. Only under 
special conditions do plant lice produce both sexes, which then 
pair. This pairing leads to the laying of eggs from which 
hatch, without exception, parthenogenetic females that give 
birth to living young. 
These observations led entomologists to search for further 
cases of parthenogenesis. It was soon discovered that certain 
butterflies, belonging to the genus Solenobia, lay unfertilized 
eggs? which develop eventually in a thoroughly normal manner 
into butterflies. Von Siebold, who repeated and confirmed 
these investigations, also found parthenogenetic reproduction 
in another butterfly, Psyche helix,® of which the males were 
quite unknown at that time. In all these cases not only were 
the larvae arising from the unfertilized eggs normal, but they 
also developed into perfectly normal sexually mature insects. 
But the greatest sensation was aroused by the observations 
of Dzierzon on parthenogenesis in bees.* He was led to the 
1 Quoted after Ratzeburg, Die Forstinsekten, Part III, 1844. 
2 We gather from von Sieboid’s monograph that these facts were first dis- 
covered by DeGeer. 
3 Von Siebold, Wahre Parthenogenese bei Schmetterlingen und Bienen, Leipzig, 
6. 
4 According to von Siebold, Dzierzon first published his observations and con- 
clusions in the year 1845 (in the Hichstddter Bienenzeitung). 
43 
