1 84 



THE EVOLUTION OF SEX. 



katabolism is indeed the ideal of all organic life. That the 

 extrusion of one polar globule still occurs, only shows that 

 some katabolic products are still expelled. In parasitic fungi, 

 sexual reproduction disappears, and surrounding waste products 

 presumably help the purpose otherwise effected by sexual 

 organs, so peculiarities in the conditions of parthenogenetic ova 

 may explain the retention of the normal balance which makes 

 division possible without the usual stimulus of fertilisation. 

 Abundant and at the same time stimulating nutrition (Rolph), 

 early differentiation of the sex-cells (Simon), the general pre- 

 ponderance of reproductive over vegetative constitution (Hen- 

 sen), their liberation before the anabolic bias has carried them 

 too far, are among these favouring conditions. The incipient 



[ disease (d) . 

 Female-^ sex (s). 



(parthenogenesis (p). 



( parthenogenesis (p). 

 ^la.\e -' sex (s). 



( disease (u). 



Diagram illustrating the theory of parthenogenesis. 



segmentation observed in a few ova is an independent effort to 

 save themselves from being too big to live, since they are not 

 passive enough to remain dormant. Waste has set in, self- 

 digestion begins, the cell is forced into the expedient of divis'ion. 

 In higher animals this is all in vain : in lower animals such im- 

 perfectly differentiated female cells are commoner ; they form 

 the parthenogenetic ova. 



§ 9. Origin of PartJieiiogejiesis. — From the occurrence of 

 parthenogenesis in the animal series, it is certain that it has 

 originated as a degeneration from the ordinary sexual process. 

 It is no direct persistence of a primitive ideal state, though to 

 some degree a recapitulation of it. One hypothetical mode of 

 origin, which may well apply to the rotifers, is easily sketched. 



