1 68 AMPHIMIXIS OR ESSENTIAL MEANING OF [XIT. 



ence. Thus, let us call to mind Phylloxera and its allies, in 

 which many purely parthenogenetic generations follow one 

 another every year and bring about an immense increase of 

 individuals, to be finally succeeded by a single sexual genera- 

 tion of insignificant wingless males and females without mouth 

 appendages, which have nothing to do but pair immediately 

 after birth in order to produce the fertilized ova. Thus, sexual 

 reproduction is retained in spite of the fact that no increase, 

 but rather a decrease, in the number of individuals is, in these 

 cases, brought about by its means, just as in the conjugation of 

 the lower unicellular organisms. Some great advantage must 

 therefore follow from its retention. 



It may, however, be lost, and we cannot at present decide 

 whether the immediate advantages which pure parthenogenesis 

 affords are sufficiently important to justify the disappearance of 

 those arrangements by which the power of increasing variation 

 is guaranteed. We cannot penetrate far enough into the details 

 of the struggle for existence to be able to determine whether 

 a species can in any way fall into so critical a position that 

 its survival can only be brought about by that excessively rapid 

 rate of multiplication which is rendered possible by pure par- 

 thenogenesis. In such a case amphigony would have to be 

 abandoned, for the only choice would be that between extinction 

 and parthenogenesis, and the future of the species would be 

 to some extent sacrificed to its temporary maintenance. But 

 I do not by any means wish to imply that this is the only way 

 in which the omission of sexual reproduction can be understood. 

 The question is only opened, and wx cannot yet claim to have 

 answered it satisfactorily. 



: We must now turn our attention for a short time to the vegetable 

 world. Unfortunately, there are not, as far as I am aware, any 

 available observations on plants which give us rehable informa- 

 tion as to those processes of maturation of male and female sexual 

 cells which have now been described in the animal kingdom. 

 Certainly Strasburger and others years ago described cell- 

 divisions of mother-cells, both male and female, which resemble 

 the ' reducing divisions ' of mother-cells in animals ; but 

 whether, in this case also, a doubling of the idants precedes 

 their twice-repeated division into halves, appears to be un- 

 known. If we may assume that such a result is by some 



