2C2 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII. 



rejuvenescence being absent, the animal grows old (senescence) 

 and finall}'' dies a natural death. I do not agree with this 

 interpretation. The significant inner changes which take place 

 during conjugation were obviously prepared some time before- 

 hand, and the micro- and macronuclei of animals which feel 

 impelled to conjugate are already in a state which must sooner 

 or later lead to profound changes of one or both— and this 

 whether conjugation has taken place or not. In either case 

 these changes will be essentially the same, — the destruction 

 of the macro- and division of the micronucleus. One thing 

 alone does not happen, — the coalescence with the nucleus 

 of another individual. But we know that all the products 

 of the micronuclear division disappear except that which 

 gives rise to the reproductive nuclei and that this is 

 always the one lying nearest the connecting bridge which 

 unites the conjugating animals. If then it is the influence 

 of another animal which renders a grand-daughter-nucleus 

 capable of further development, we are led to conclude that 

 such an influence is lost when conjugation does not occur. 

 In this, I believe, lies the cause which leads the vital energies 

 to grow weaker and finally to cease, in the descendants of an 

 animal which has undergone the changes described above. 

 It is the same with the ovum,— the processes of maturation 

 which prepare for fertilization, produce changes which prevent 

 the future life of the egg-cell, unless it be fertilized. 



Maupas will reply that it has not yet been proved that such 

 changes appear when conjugation is absent : he has never 

 observ'^ed them in the Infusoria which he prevented from 

 conjugating. He did not make the observation because he 

 regarded the changes as phenomena of age. It now remains 

 to follow accurately the alterations which appear in the 

 macro- and micronuclei, when a colony has been prevented 

 from conjugating. The observations will be difficult, because 

 they must extend over many generations ; for the end of the 

 period favourable for conjugation cannot be foretold with 

 certainty and, according to Maupas, is not reached in all the 

 animals of a colony at the same time. 



My interpretation does not by any means require that the 

 changes in animals prevented from conjugating, should follow 

 precisely the same course and pass through exactly the same 



