THEORY OF FERTILISATION. l6l 



as essentially one of mutual digestion. His vivid words weL 

 deserve quotation : — 



" Conjugation occurs when nutrition is diminished, whether this be due 

 to want of light, or to the lowered temperature of autumn and winter, or 

 to a reduction of the organisms to mimimal size. It is a necessity for 

 satisfaction, a gnawing hunger, which drives the animal to engulf its 

 neighbour, to 'isophagy.' The process of conjugation is only a special 

 form of nutrition, which occurs on a reduction of the nutritive income, or 

 an increase of the nutritive needs, in consequence of the above-mentioned 

 conditions. It is an 'isophagy,' which occurs in place of 'heterophagy.' 

 The less nutritive, and therefore smaller, hungrier, and more mobile 

 organism we call the male, — the more nutritive and usually relatively more 

 quiescent organism, the female. Therefore too is it, that the small starv- 

 ing male seeks out the large well-nourished female for purposes of conjuga- 

 tion, to which the latter, the larger and better nourished it is, is on its 

 own motive less inclined." Cienkowski has also inclined to a similar view, 

 regarding conjugation as equivalent to rapid assimilation. 



Simon also seeks to establish the following among other vague con- 

 clusions : — Sexuality has, he says, arisen twice (we should say much oftener), 

 once among plants, again among Protozoa. Two similar cells unite ' ' in order 

 to reach the limit of their individuality." In both kingdoms the union is 

 at first protective, though in a different fashion in the two cases. In the 

 progressive differentiation, these two sex-cells are usually so constructed 

 that the loss of substance in the union is reduced to a minimum, hence the 

 small mobile male and the large quiescent female cells. The union brings 

 about a chemico-physical process, which makes the female cell capable of 

 independent nutrition and growth, and evokes potential properties into 

 actual life. 



In marked contrast to Rolph's suggestion, and the view of all 

 those who believe that the sex-cells are profoundly different, is 

 the opinion maintained by Weismann. He denies that there 

 is a dynamical action in fertilisation. The momentous effect is 

 merely the sudden doubling of the mass of the nucleus. " The 

 physiological values of sperm and egg-cell are equal ; they are 

 as I : I. We can hardly ascribe to the body of the ovum 

 a higher import than that of being the common nutritive basis 

 for the two conjugating nuclei." The external differences which 

 are so obvious are only important as means towards the con- 

 jugation of similar nuclei. "The germ-plasma in the male and 

 female reproductive cells is identical." Previous to the essential 

 moment of fertilisation, half of the germ-plasma is given off 

 from the germinal vesicle of the ovum in forming the second 

 polar body. Development will not take place unless the loss 

 be made good, and the original mass restored. This is what 

 the sperm does in fertilisation. In short, to Weismann the 

 process is quantitative rather than qualitative. 



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