PRESIDENTIAL ADDRESS — SECTION D. 187 



It is generally acknowledged that, in such simple organisms 

 as Amoeha, reproduction, in the form of fission, is, primarily 

 at least, the direct outcome of overgrowth : the mass becomes 

 too great for the surface, and becomes divided into two. No 

 doubt this process of division, being advantageous for preserva- 

 tion, has become to a considerable extent hereditary, and 

 multiplication may, accordingly, in many instances take place 

 before the necessity for it owing to overgrowth becomes 

 pressing. 



Eyder's view is that this cumulative integration acts as a 

 motive force in developing sexuality, not only in its simple 

 forms but in all the phases of its increasing complexity as we 

 ascend the animal and vegetable series. At first, the cleavage 

 which followed from overgrowth, in order that the metabolism 

 of the protoplasm might go on with advantage (the proper ratio 

 of surface to mass being maintained), resulted in the formation 

 of small parts or division -masses, which became completely 

 separated off from one another as independent organisms. 

 In the lowest forms the w^hole oi'ganism consists of a 

 single variety of living substance ; but in all above the 

 lowest there are two distinct varieties sharply marked off 

 from one another, and present in very unequal proportions. 

 In the former the process of division is direct ; while in the 

 division of the latter there is a reaction between the two 

 kinds of living substance, "which is expressed most strongly 

 as karyokinesis." 



The effect of overgrowth in unicellular organisms has been 

 to ijroduce a preponderating quantity of plasma, which in- 

 vests the primitive nuclear plasma or chromatin with a thick 

 envelope — the cell-body or cytoplasm — and this provides a 

 field for the reaction of the two forms of living matter in the 

 phenomena of karyokinesis. 



This increase in the quantity of cytoplasm was due to the 

 rapidity of growth, by which suflicient time w-as not allowed 

 for conversion into nucleoplasm or chromatin rapidly enough 

 for the division into smaller parts by the direct process of 

 fission. Though at first, as already mentioned, the division- 

 masses produced as a consequence of overgrowth became at 

 once separated from one another, there arose with the increase 

 of cytoplasm a tendency in some cases for the masses to 

 remain in cohesion. There came thus to arise two sorts of 

 division resulting from overgrowth— cZ/sr^p^/rc and coherent. 



The development of a cell-body led to the production, by 

 divergent evolution, of two sorts of cells. One of these — the 

 most primitive — was poorly provided with cell-protoplasm. ■ 

 This became the male cell. The other was a cell arrested on 

 its way towards disruption into male cells — a cell which, owing 

 to the effects of overgrowth, had lost its tendency to break up 



