136 THE EVOLUTION OF CONTINUITY 



as Natural Variation. The determination of Sex is still 

 an obscure question, whose solution is at present being sought 

 on Mendelian lines ; but although we have as a result the 

 ingenious Chromosome Theory, the broad significance of 

 Unisex has not so far revealed itself. The limits of this 

 book do not allow us to include, as was at first intended, 

 a summary of Mendelism and the light it throws on the 

 transmission of characters and variations, but we would 

 state the following general conclusions of our own, which 

 need not clash with observed Mendelian phenomena : — 



In the simpler forms of living Continuity the develop- 

 ment of the Individual ends in the restoration of both male 

 and female elements, but in the higher forms, where Arrest 

 is more rigid, and tissue-differentiation more complex, only 

 one type of sexual element is reproduced. But the Individual 

 evolves from the fusion of male and female elements, which, 

 we may say, are equally desirous of being reproduced ; 

 and it does not seem unreasonable to suppose that while 

 the restoration of one of these goes on to the end along 

 the main road of cycle evolution, that of the other is diverted 

 along the side-paths leading to the fixed somatic cell-species. 

 Or we might suppose as an alternative, that its restoration 

 lags behind so that it is incomplete when the body is mature. 

 The case of the queen bee lends some colour to the latter 

 supposition, as it would appear that by the time her true 

 ova are formed " her " male elements are still on the road 

 to being reproduced : hence the development of " drone- 

 tissue." The case here is in fact suggestive of " dichogamy " 

 in certain aspects, and it is to be noticed that the queen bee 

 cannot be fertilised by her fresh generation of drones. 



As the offspring must vary from the parents, it is obvious 

 that the offspring of different pairs of parents cannot exactly 

 resemble each other. But more mysterious is the variation 

 between the successive offspring of the same parents. This 

 cannot wholly depend on the main natural variation of 

 Sex, for brother varies from brother, and sister from sister, 

 as well as brother from sister. It would indeed seem probable 

 that Acquired Variation enters considerably into the question. 

 Even if we suppose that all the male parent's spermatozoa 

 are equal in potentialities, and similarly all the female 

 parent's ova, it seems clear that the modifying influences 



