SEX AND HEKEUn V 



quoted showing similar examples of difTcrentiatio:. . (Pig. 



335). The question naturally arises why should such p- 



in a plurality of distinct phyletic lines? That the d::. 



sex has occurred more than once indicates a probability that some 



real advantage has prompted it. 



The advantage appears to lie in the fact that the larger the amount 

 of nutriment embodied in the egg, the better nourished the offspring 

 will be in its first stages, and the better accordingly will be the - * 

 of its passing successfully through the dangerous rislcs of . 

 But the larger the egg the less mobile it will be. Even in the hquid 

 medium into which the eggs of Algae are often shed, a large body is 

 less easily moved than a small one. We naturally associate with this 

 the fact that the larger eggs have lost their motility. This is, how- 

 ever, immaterial so long as the spermatozoids remain small and 

 actively motile, provided that the egg can influence their movements, 

 and so act as a centre of attraction to them. It hiis been seen that 

 the eggs are able to do this (p. 386). Such advantages as follow from 

 the stimulus of fusion, and the pooling of the hereditary factors of 

 the two sexual cells can still be secured by these means. Thus the 

 nett advantage lies with the plant which can, without sacrificing 

 the benefits that follow from syngamy, secure also for its oflfspring an 

 increased probability of successful germination. Conjugating organ- 

 isms, with their small equivalent gametes, maybe regarded as a plant- 

 proletariat that produces numerous offspring with little physiological 

 capital ; so that each individual must depend chiefly upon its own 

 efforts. The organism that shows differentiation of its gametes 

 with an enlarged well-nourished egg is like a capitalist, whose pro- 

 geny starts life well furnished with an inheritance. Other things 

 being equal, ultimate success will lie with the latter. Both King- 

 doms of Living Beings show how successful the results of scx- 

 differcntiation have actually bcon ; fnr ..11 iluir lii-luT tcrin> h.ivr 

 differentiated gametes. 



A large naked egg, such as tiiat ui J-'utus, may be .1 

 enough means of propagation in water. But it rouid : > 



into an embryo exposed to the drying influence 

 A necessary condition of Life on the Land is thus lac jr 

 one way or another of the egg and the embryo. In the . ;» 



of Land-living Plants and Animals this necessity has played a 

 leading part. The result is seen in the various forms of interna! r**-^'- 

 ology : that is, the envelopment of the egg an'l of tlu- rinbr>-o - 

 the tissues of the parent. This brings al.so \' .idvaiilu|;c 



