374 Experimental Zoology 
In certain moths, Solenobia triquelrella and S. lichenella 
and Psyche helix, a succession of parthenogenetic females has 
been known to occur. In the first two species males may not 
appear for years, and then suddenly appear, and even excede the 
females in numbers. In one group of Rotifers, Philodinide, 
males have never been found. In other families small, semi- 
parasitic males may be present, but it is believed that in some 
of these cases these minute males do not fertilize the eggs. 
Whether the males have thus slowly disappeared or have sud- 
denly ceased to appear in the Philodinidz is not known or even 
surmised. 
In still other insects parthenogenesis occurs. The larva of 
the fly, Miastor, produces eggs that develop within its body and 
produce there young maggots. This method may go on for 
several generations, but ultimately some of the larvee pupate and 
the sexually perfect flies emerge. The conditions that determine 
which mode of production takes place have not been determined. 
In the gnats of the genus Chironomus, the pupa deposits eggs, 
but the pupa is in reality an imago that does not ordinarily 
leave its pupa skin. Thrips seem to reproduce by partheno- 
genesis throughout a part of the year. Some caddis flies are 
said to be parthenogenetic. The walking sticks of the genus 
Bacillus also produce as a rule by parthenogenesis. In Bacillus 
Rosii only 1 male and 20 females were found to emerge in 
one case from parthenogenetic eggs. In some moths and butter- 
flies, parthenogenesis occurs either as a regular or as anoccasional 
process. Parthenogenesis has already been described in the 
gallflies, and other cases in the hymenoptera will be described 
later. In other groups of animals, parthenogenesis is also’ 
known, as in the Trematodes, for instance; but the group of 
insects furnishes the most striking cases of this method of repro- 
duction. 
