200 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



suggested that with insects like saw-flies, complete 

 parthenogenesis — that is, leading to the production 

 of females only — was of greater utility to the species 

 than if males were produced. I pointed out that 

 with species like the Gooseberry Saw-fly, large 

 numbers of males might be born without there 

 being any females with which they could mate ; 

 that if only females were produced, the reproductive 

 power of the species was doubled ; and further, that 

 in those species where parthenogenesis existed, the 

 males were rarer than usual, some being exceedingly 

 rare, while other species appeared to be completely 

 without males. As regards the first point, the 

 following observation is of interest. In my garden 

 the gooseberry-grub was tolerably common in the 

 early summer last year. In due course numerous 

 males appeared from this first brood ; but careful 

 observation, extending over two weeks, failed to 

 reveal a single female, nor did a solitary larva show 

 itself on the bushes, thus proving that the yield of 

 this brood was entirely male. This observation is 

 in harmony with others of a like nature, and tends 

 to prove that parthenogenesis of this kind may be 

 actually injurious to the species, which, if it is to 

 live, must either revert to sexual generation, or get 

 rid of the males entirely, as we know many species 

 have done. But while I pointed out that agamic 

 reproduction was of greater utility to the species 

 than mixed parthenogenesis, yet at the same time I 

 gave reasons for believing that parthenogenetic 

 species had less vigour and vitality, and could not 

 withstand so effectually the attacks of insect or 

 fungoid enemies or climatic variations — in other 

 words, they maintained their existence only by their 

 greater reproductive power. If, on the one hand, 

 we have abundant evidence of a higher development, 

 which may be structural or mental or both, on 

 the other hand there is equal evidence of a retro- 

 grade development in organic life. Parthenogenesis, 

 in my opinion, in the case of most insects, must be 



