THH CYNIPID.E AFFECTING THli OAK. 31 



but as years passed investigations made by other 

 naturalists (Sars, Siebold, and Loven) proved that he 

 was correct. 



In 1842 J. J. S. Steenstrup pu1)lished (' tJber den 

 Generationswechsel ') all that was known on the sub- 

 ject. The essay was translated into English by George 

 Rusk, and published by the Ray Society, 1845. Steen- 

 strup quaintly descril^es this mode of reproduction as 

 " a peculiar form of fostering the young of the lower 

 classes of animals." The preface {Joe. cif, p. 1) contains 

 the following paragraph : " Alternation of generations 

 is the remarkable, and till now inexplicable, natural 

 phenomenon of an animal producing an offspring, 

 which at no time resembles its parent, but which, on 

 the other hand, itself brings forth a progeny, which 

 returns in its form and nature to the parent animal, so 

 that the maternal animal does not meet with its 

 resemblance in its own brood, but in its descendants 

 of the second, third, or fourth degree or generation." 



The bi-sexual, therefore, gives rise to the asexual or 

 agamic, and the agamic in its turn to the bi-sexual. 

 Moreover, the two generations produce galls which 

 differ entirely in shape, size, and situation. 



One generation consists of females only, the other 

 includes ])oth males and females. The bi-sexual insect 

 is the result of the union of the male and female, the 

 agamic when that condition is absent. 



The theories of non-sexual reproduction are very 

 complex. The facts, however, are simple. From 

 many oak galls which mature^ in the spring or early 

 summer females only emerge, and without assistance 

 of the male they lay eggs from which larvae hatch. 

 This is known as parthenogenesis, a word given to the 

 phenomenon by Professor Sir Richard Owen. The 

 galls caused by these larvas mature in early autumn, and 

 from them there issue both male and female imagines, 

 from the union of which eggs are deposited, and the 

 resultant larvas produce galls like their agamic grand- 

 parent. The ability to reproduce parthenogenetic eggs 



