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, Philodinidae, 

 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 Philodinidae 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 larvae 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 i 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 an occasional 

 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. 



