THE GENERAL SIGNIFICANCE OF AMPHIMIXIS 213 



Assuredly the whole intricate complex of adaptations whicli 

 is now exhibited on the conjugation of the two sex-cells in animals 

 and plants, the differentiation of two kinds of ' sexually ' antagonistic 

 cells, with all their special adaptations, the reduction of the chromo- 

 somes, the institution of the karyo-kinetic apparatus, together with the 

 centrospheres and so on, cannot possibly have arisen all at once by 

 fortuitous variation, but can only have arisen gradually, step by step, 

 and as the result of 'innumerable external and internal influences.' 

 But why should not these arrangements, nowadays so complex, have 

 had a simple beginning ? Why might not this beginning have been 

 the simple union of the protoplasmic bodies of two non-nucleated 

 Monera ; followed, after the origin of nuclear substances, by the union 

 of these, and, finally, after the differentiation of a nucleus with 

 a definite number of chromosomes, with a dividing apparatus, with 

 a membrane, and so on, by complete amphimixis as we now know it ? 

 And how many transition stages may not be added to fill up the 

 gaps between these three main stages ? 



But how much we can actually prove in regard to these con- 

 ceivable preliminary stages of amphimixis is another matter. If we 

 take a survey of the observations that have been made up till now, 

 we are confronted at first by the undoubtedly striking fact that verj' 

 little is known about it as yet, for in fact the whole process is gone 

 through even in quite lowly forms of life in a manner very similar to 

 that in the higher forms. Amphimixis has been shown to be wide- 

 spread even among unicellular organisms, yet not in an essentially 

 simpler mode than among multicellulars. We have seen that even in 

 ciliated Infusorians reducing division obtains, and that of the four 

 nuclei which arise from twofold division of the original nucleus 

 three break up again, and only the fourth, by a further division, 

 separates into a male and a female pronucleus, 'which then com- 

 plete the amphimixis with the corresponding pro-nuclei of another 

 animal' (compare Fig. 85, 4-7, vol. i. p. 321). This, and the existence 

 of a dividing apparatus and of chromosomes, make the process appear 

 very little less complicated than the fertilization of higher animals. 

 The case is similar even in much lower unicellular organisms, such as 

 Noctiluca (Fig. 83, vol. i. p. 317). In this form and in Rhizopods it is 

 true that reducing divisions have not yet been made out, but their 

 occurrence in the lower Algffi (Basidiobolus), and above all in those 

 simple unicellular organisms which give rise to malaria, and their 

 allies, which live as ' Coccidia ' in the blood-cells and intestinal cells 

 of animals, leads us to expect that they may prove to be of general 

 occurrence among unicellulars. 



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