62 Heredity. 



lay eggs as soon as they have passed through the pupa 

 stage. These parthenogenetic eggs give rise only to fe- 

 males, and these may give rise to female descendants in 

 the same way for an indefinite number of generations; 

 3d, in at least one species (Solenobia triquetrella), the 

 eggs which are laid by impregnated females give rise to 

 both sexes. 



Dnfur, Kessler, Hartig, Walsh, and many other nat- 

 uralists have shown that certain female gall-wasps are 

 parthenogenetic; within recent years Bassett and Adler 

 have made most interesting observations upon these 

 wasps. In 1873 Bassett showed (Canadian Entomolo- 

 gist, 1873-75, p. 91) that great numbers of male and 

 female wasps escape in June from certain galls which 

 are found in very great abundance on the leaves of an 

 oak. Late in the summer the females lay their eggs 

 in the leaves of the same oak, and give rise to galls, 

 which, however,. are of quite a different character from 

 those in which the insects were born. Early in the fol- 

 lowing spring a brood of females hatch from these win- 

 ter galls, and at once lay parthenogenetic eggs, which 

 give rise to the summer galls, and hatch in June into 

 males and females. 



Bassett and Adler have extended these observations to 

 a great number of species, and the following account is 

 taken from a paper by the latter writer ("Ueber den 

 Generation swechsel der Eichen-Gallwespen," von Dr. H. 

 Adler, Zeit. f. Wiss. Zool, xxxv. 151), who has carried 

 on a long series of the most painstaking experiments, 

 using every precaution against error. 



He reared a great number of small oak-trees under 

 glass cases, and then, introducing the wasps, traced their 

 whole life history, and he found that in many species 

 there is a winter gall, which is produced in the fall by a 



