THE GEXERAL SIGNIFICANCE OF AMPHIMIXIS 203 



older than all .species-characters, older than the chaiacters of tlie 

 o-enus, of the familj', of the class, and indeed of the whole series 

 or phylum to wliich a higher animal, a vertebrate, for instance, 

 lielongs. We cannot wonder, therefore, that amphigony has persisted 

 through hundreds and thousands of generations, even if it had not 

 been reinforced in the germ-plasm during this period by selection. 

 We should rather wonder that an institution so primaeval, and so 

 firmly engrained in the germ-plasm, can ever be departed from, even 

 when its abandonment is to the advantage of the species, as has 

 happened in parthenogenesis. 



I have entered upon this long discussion because I believe that 

 we require to appreciate this poAver of persistence on the part of the 

 sexual determinants before we can explain the general occurrence of 

 amphigony. The occurrence of pure parthenogenesis, unaccompanied 

 by any degeneration of the species, can hardly be understood except 

 on the assumption that the constancA^ of the species, when it ha.s once 

 been attained, may be preserved without the continual intervention of 

 amphimixis. How long it can be preserved is another question, which 

 it is difficult or impossible to an.swer, since .species exhibiting pure 

 parthenogenesis are rare, and since we cannot tell with ceitaintj' how 

 long it is since amphimixis ceased to occur in them. Generally 

 speaking, the answer in regard to the few .species which have to be 

 taken into account in this connexion would be ' not long,' but whether 

 this 'not long' signifies hundreds of generations or thousands of 

 generations we must leave undecided. So much only we can saj', that 

 in all species of animals in which the male sex has quite died out or 

 has dwindled to a minimal remnant, there are as yet no traces of 

 degeneration to be found, and that even organs which have fallen into 

 disuse and become functionless because amphigony has disappeared, 

 are nevertheless in several cases retained in perfect completeness. I 

 shall return to this subject later on, but in the meantime I wish 

 to work out our conception of the actual efficacy of amphigony or 

 ordinary sexual reproduction, and thereby increase our understanding 

 of its significance and power of persistence. 



We have seen that amphigony not only renders possible the novel 

 ' harmonious adaptations ' which are continually required, but that it 

 also leads, by a continual crossing of individuals, simultaneously with 

 the elimination of the less fit, to a gradually increasing constancy of 

 the species. This has been regarded hy some writers as its sole effect : 

 thus recently by Hatschek, whose view has already been refuted. 



Haycraft also finds the significance of amphigony simply in the 

 equalizing or neutralizing of individual differences which it effects. 



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