Xil.J CONJUGATION AND SEXUAL REPRODUCTION. 203 



stages as those which occur in conjugated animals. This 

 is a priori very improbable. We must not forget that the 

 interval between two successive conjugations extends over many 

 generations, and that those inner conditions which prepare 

 for conjugation are gradually built up, reach their highest 

 point, and are then lost. If, when the appropriate period 

 has arrived, conjugation takes place, the long-prepared pro- 

 cesses of maturation take their normal course ; but if this period 

 is passed by, the whole future development is abnormal. The 

 animal increases a hundredfold or more, but development 

 cannot pursue its normal course, the nucleus degenerates, — 

 sometimes the macronucleus being the first, sometimes the 

 micronucleus, — and finally neither assimilation, nor the main- 

 tenance of the characteristic body-form can be kept up, 

 and the animals die one after the other. The irregularity in 

 the course of these phenomena, as Maupas describes them, 

 points to the fact that we are concerned with an abnormal 

 process. 



Does Natural Death occur in Unicellular Organisms ? 



Why do some writers regard the process described above 

 as the equivalent of the normal death of Metazoa 1 Merely 

 because of the traditional dogma which asserts the necessity of 

 normal ' physiological ' death. They overlook the fact that in 

 Infusoria conjugation is a normal process^ the periodical re- 

 currence of which is provided for by nature, and upon which 

 the whole vital mechanism of these animals is, to a certain 

 extent, regulated. Nature must have amphimixis, and brings 

 it about by the internal changes which impel the animals to 

 pair, and by those which gradually render them unable to live 

 when conjugation is artificially prevented. It is, as I have 

 already argued, precisely equivalent to the effects which follow 

 the non-occurrence of fertilization. The spermatozoon which 

 fails to find an ovum, dies. If anyone finds pleasure in bring- 

 ing confusion into ideas which have just become to some extent 

 clear, he may speak of this as the ' normal death ' of the sperma- 

 tozoon ; I call it an accidental death, although I am well aware 

 that this unhappy accident is far more common than the success- 

 ful attainment of the normal object of a spermatozoon's life. In 

 most animals millions of spermatozoa are lost before a single 



