C. DOBELL 139 



CHAPTER II. 



The Life-cycle of a Ciliate according to Maupas. 



16. I propose in this chapter to state very briefly the chief general 

 conclusion.? drawn by Maupas from the extensive investigations which 

 culminated in his great works of 1888 and 1889. His clear and precise 

 conceptions will form a convenient fixed point from which to contem- 

 plate the work which has since been done. 



17. Maupas claimed to have proved that the lives of ciliates run 

 in cycles'. There is first a period of asexual multiplication (agamic 

 period, or period of immaturity), during which the progeny of an 

 exconjugant continue to multiply, without conj ugating . or being able 

 to conjugate. At the end of this period — of definite length for each 

 species — the organisms attain the age of puberty, after which con- 

 jugation is possible and normally occurs in nature. Unless they 

 conjugate, the organisms continue to multiply for a further definite 

 number of divisions. This second period — during the whole of which 

 the animals are sexually mature — is called by Maupas the eugamic 

 period. If, for any reason, conjugation does not occur during this 

 period, the animals now enter a third period of multiplication — the 

 period of senescence — which is also of definite duration. Throughout 

 this period the animals suffer more and more froin old age, until they 

 finally die after completing a given number of fissions. Those organisms 

 which are able to conjugate successfully during the eugamic period 

 become " karyogamically rejuvenated," or reorganized, and start another 

 cycle of development like that just described. 



' This view was first definitely expressed — so far as I am aware — by Claparede and 

 Lachmann (18(50) and by Balbiaui (1860). It has been stated by Woodruii (190!1 a) that 

 Dujardin "maintained that the life-history of infusoria comprises a cyclical change iu 

 vitality which terminates in death." I know of no passage in his writings which can 

 be construed in this fashion. He certainly did not believe in a "cycle" such as that 

 described by Maupas, for he held that a sexual act had not been proved to occur in any 

 ciliate. Dujardin (1841, p. 87), suggested that there is possibly a limit to multiplication 

 by fission, but he did not maintain this proposition or take sides on the issue. Balbiani's 

 statements, however, are very definite. He says that he has established the fact that 

 there is a limit to asexual reproduction in the ciliates. The period of asexual multiplica- 

 tion terminates with natural death of all individuals belonging to the same cycle ; or " by 

 a return of sexual reproduction, indicating the completion of one of these cycles and the 

 beginning of a new cycle"; or by encystation. (See Balbiani, 1860.) His views were 

 therefore at this time — he frequently changed them — very similar to those of Maupas. 



