226 LECTURES ON BIOLOGY 



new sources of energy without which the existing life-machine 

 would inevitably perish. 



But though this explanation sounds clear we must not forget 

 that in test-tubes we offer to the ParamcBcium very different con- 

 ditions from those that obtain in free nature. Moreover, in the 

 last-mentioned case we deliberately continually overfed the 

 animalcules in order to prevent the union. It is, therefore, at 

 least as probable tbat the gradual degeneration and the final 

 extinction of the colony can be referred to these factors, as that 

 the cause is to be found in our having prevented conjugation. 

 I am rather inclined to agree with Weismann, who says that the 

 importance of conjugation lies in the amphimixis, in the exchange 

 of the characters of two different individuals, and the increase 

 in variability and adaptability conditioned by it. 



Let us now endeavour to find out with the aid of the micro- 

 scope what conjugation really is, and what happens during this 

 process (fig. 56). Soon after the animals have taken up a 

 ' mouth to mouth ' position their nuclear apparatus shows 

 characteristic changes. The macronucleus which, as we have 

 already seen, controls tbe ' vegetal ' functions of cell-life is 

 not in any way affected, but in the micronucleus we notice 

 far-reaching alterations. At first it divides indirectly into two 

 daughter-nuclei which immediately divide again. It must be 

 remembered that all these processes take part in both con- 

 jugated animalcules in the same manner. We see therefore in 

 each in place of one uniform micronucleus four daughter- 

 nuclei, but very soon three of these once more perish and are 

 disintegrated in the protoplasm, while the fourth once more 

 divides into two nuclei. But though identical in appearance, 

 their destiny is very different. We distinguish them by calling 

 one the ' female/ the other the ' male ' nucleus. 



Though our observation has already taken up several hours 

 we must not lose patience, because the most important process 

 is yet to come. In the region of the mouth-aperture a small 

 plasm-bridge has formed between the two Paramcecia, and now 

 we see that the male nucleus of A wanders into the proto- 

 plasm of B, and vice versa. The two united individuals therefore 

 exchange their nuclear substance. When that has been done the 

 Paramcecia once more separate and each travels its own road, in 



