SIGNIFICANCE OF CONJUGATION 201 



as it does in P. caudatum, and it is doubtful whether it is 

 eventually resorbed or whether it fuses with one of the new 

 macronuclei. 



The phenomena of conjugation in Paramecium caudatum 

 are worthy of most careful study, for they have been worked 

 out more carefully in this species than in any other Protozoan, 

 thanks chiefly to the brilliant researches of Maupas. Com- 

 paring the course of events with those observed in Bodo, 

 Polytoma and other Protozoa, it will be observed that in 

 Paramecium there is no distinction of sex as far as the two 

 gametes are concerned. Both are exactly alike and equal in 

 size. But there is an indication of differentiation in the 

 micronuclear products, so that we have not hesitated to call 

 the active product the male and the passive one the female 

 pronucleus. Again, it is remarkable that the conjugation is 

 only temporary, the two gametes separating and dividing, each 

 on its own account, after the mutual transfer of micronuclear 

 material has been effected. There is no fusion of cytoplasm, 

 and no zygote is formed. Perhaps the most instructive com- 

 parison is that between the conjugations of Paramecium and 

 Monocystis. The abortive products of the first two micro- 

 nuclear of divisions in Paramecium are comparable with the 

 so-called polar bodies of Monocystis, and in the latter form 

 the conjugating individuals preserve their individuality to some 

 extent, though not as completely as in Paramecium. In Mono- 

 cystis the gametes encyst before any exchange of nuclear 

 material takes place, and are therefore called zygotes, in contra- 

 distinction to the gametes of Paramecium which do not encyst. 

 Perhaps the most striking result of Maupas' researches is 

 the evidence, more surely founded than in the case of Polytoma 

 or Bodo, that in Paramecium and a large number of other 

 ciliate infusoria there is a definite limit to the reproductive 

 faculty, and when this limit is reached death ensues if conjuga- 

 tion does not intervene to restore the lost fertility. It would 

 appear that in these lowly organised creatures there is, as in 

 the higher animals, a period of growth, of bloom, and of decay ; 

 that the organism wastes and wears out in the exercise of its 

 functions, and requires rejuvenation from time to time in order 

 that its activities may not be brought altogether to a stop. 

 This rejuvenation is effected, in a manner unknown to us, by 

 the act of conjugation, and Paramecium shows, better than 



