VII PARTHENOGENESIS 247 



develop each into a new individual. Why should 

 it be that in certain cases these last require fusion 

 with another peculiar kind of cell elements before 

 they will develop) ? Some light seemed to be thrown 

 on this matter at first, by the observation that the 

 unfertilised ova of the bee always produce drones, and 

 that only the fertilised produce females ; but this indi- 

 cation of a possibly clearer insight into the matter is 

 entirely upset by the fact, now fully established in the 

 present work, that in some species of insects and crusta- 

 ceans the unfertilised ova always, or in an enormously 

 large proportion, produce females only ; whilst in the 

 Aphides we know that they ultimately produce both 

 males and females. Mr. Darwin has suggested the 

 most satisfactory theory of fertilisation, in assigning to 

 it the object of fusing two life-experiences in the pro- 

 geny, which thus gains tendencies and acquires im- 

 pulses from a wider area than does an unfertilised 

 ovum, and is in so far strengthened. Conjugation of 

 two cells, similarly formed but belonging to different 

 individuals (as seen in Confervse and Gregarinae) is 

 the simplest arrangement for obtaining this end ; the 

 only difference between this and sexual reproduction 

 is that in the latter process one cell seeks, the other is 

 sought; and this differentiation into active and passive, 

 the wooer and the wooed, commencing in the simplest 

 vegetable and animal cells, persists to the highest rank 

 of development. Self-impregnation (if it have a real 

 physiological existence) and parthenogenesis, have, 

 then, to yield, as chief modes of reproduction, to gamo- 

 genesis, or the concurrence of two individuals ; and 



