Life-cycle of Some Hymenopterous Insects 357 



of which were males, but two queens also appeared. Reichen- 

 bach started with eleven workers of Lasius niger. They laid 

 eggs that became typical workers. In August, when the sexual 

 forms appeared in the out-of-door nests, about a dozen males also 

 developed in the artificial nest, although none had developed 

 before. After a few weeks the ants continued to increase in 

 numbers, and in the following year produced two to three dozen 

 males and as many as 300 workers. The same appearance of 

 males took place in the third year. 



Another case has been given by Mrs. Comstock for Lasius 

 niger in which workers appeared in an artificial nest containing 

 only workers. The queen of this species is so much larger 

 than the workers that a mistake as to the character of the 

 individuals Avas not possible. 



In another group of the Hymenopterous insects, the Tenthre- 

 dinidae, or sawfiies, some curious cases of parthenogenesis are 

 known. As a rule, in this group the males are much less numer- 

 ous than the females. The common currant sawfly, Nematus 

 ribesii, produces parthenogenetic progeny which is nearly always 

 of the male sex. It is said that on rare occasions an unfertilized 

 egg becomes a female, a point of some interest in connection with 

 the case of the bees. 



Doncaster has recently given some observ^ations of his own, 

 and reviewed the results of others in regard to the sex of saw- 

 flies from parthenogenetic eggs. He points out that according 

 to all observers females alone arise from virgin eggs of Croesus 

 varus and Psecilosoma luteolum, only one observer ever having 

 seen a male. He quotes Mrs. Chawner to the effect that she has 

 bred thousands of the latter species for several years in succession 

 without obtaining males, and without finding any diminution 

 in the fertihty of the females. Hemichroa rufa "is known to 

 give chiefly females from virgin eggs, but occasionally males are 

 produced." On the other hand, certain species produce males, 

 as a rule, from parthenogenetic eggs. Cameron states that Ne- 

 matus pavidus yields only males from unfertihzed eggs. In 

 Nematus ribesii (N. ventricosus of von Siebold) it has generally 



