THE GEXESIS OF SEX. 173 



to an ovary, but not a true ovary, these larvae end another generation 

 of larvae like themselves, which in their turn, by internal budding, 

 form a third generation, and so on until autumn, when the last genera- 

 tion develop into perfect winged insects, male and female. These 

 last cooperate to produce eggs which hatch next spring, to commence 

 another cycle of changes. 



Here, then, we observe as before the lower form of reproduction in 

 the larva, and the higher in the perfect insect. Here, again, we have 

 non-sexual mode preceding the sexual mode in ontogenesis, suggesting 

 a similar succession in phylogenesis. But in addition we observe 

 here that the form of non-sexual reproduction very closely simulates 

 sexual reproduction ; for the budding is from an internal organ set 

 apart for the purpose and very closely resembling a true ovary. 



The next step in the chain of approximation is found in imrtheno- 

 genesis or virgin generation. This consists in the formation, in a per- 

 fect female capable of sexual generation, of ovules which develop into 

 embryos loithout the cooperation of the male element. In bees and 

 wasps the ovules are sometimes fertilized and sometimes unfertilized. 

 The fertilized eggs always produce females, the unfertilized always 

 males. In this case the analogy to non-sexual reproduction is not close ; 

 because the female is, of course, the sex absolutely necessary to carry 

 on the succession of generations, and it is this sex which it requires 

 fertilization to produce. But in other cases, for example, in certain 

 moths and in some j)hyllopod crustaceans, according to Siebold, the 

 unfertilized eggs produce females and the fertilized males. In such 

 cases, it is evident, a succession of females may be formed without the 

 cooperation of the male ; and thus we have continuous generation 

 which is completely intermediate between sexual and non-sexual. It 

 is sexual in that an embryo is developed from an ovule formed in a 

 perfect ovary, it is non-sexual in that the cooperation of the male ele- 

 ment is unnecessary even for an indefinite succession of generations. 



On the other hand, the case of moths and phyllopod crustaceans 

 a]iproaches equally the case of aphids already mentioned — so much so, 

 indeed, that the larval reproduction of these latter have often been 

 classed under parthenogenesis. The difference is this : true partheno- 

 genesis takes place in perfect females, capable of sexual union and of 

 fertilization, possessing perfect ovaries and producing true ovules which 

 develop into embryos without fertilization. The larval aphid, on the 

 contrary, is not a perfect female, is not capable of sexual union nor of 

 fertilization ; its ovary-like organ is not a true ovary, does not produce 

 true ovules which develop into embryos, but forms an embrj'o at once 

 within, which then is born in an active state. Still the resemblance to 

 parthenogenesis is undoubted, and together they almost wholly fill up 

 the gap between the sexual and non-sexual modes of reproduction. 



There is still another fact which must be brought forward to fill 

 this gap. True sexual reproduction, as we have seen, consists essen- 



i 



