ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 585 



completely. A "reduction" or halving of the chromosomes (ineiosis) 

 may occur during the micronuclear divisions which take place at the 

 beginning of conjugation. It is possible that a certain amount of 

 cytoplasm is exchanged during conjugation. 



A Ciliate is a non-cellular complete organism, homologous with an 

 entire metazoon, not with a cell of a metazoon. The meganuclear 

 system is the equivalent of the nuclei of the somatic cells of a metazoon, 

 and the micronuclear system of a Ciliate is the equivalent of the germ- 

 cell nuclei of a metazoon. Conjugation is a process of reciprocal 

 fertilization, coupled with a process of complete reorganization unlike 

 anything known to occur in other organisms. The exconjugant is a 

 zygote of a very remarkable kind, for it is the remains of the " parent " 

 organism reorganized after the addition of a foreign nucleus. Forms like 

 Paramecium may be regarded as hermaphrodite individuals ; forms like 

 Vorticella show male and female individuals. All " generations " are 

 produced asexually, by fission or budding. 



The second chapter deals with the life-cycle of a Ciliate according to 

 Maupas. There is first a period of asexual multiplication and imma- 

 turity ; then the organs become sexually mature and are able to 

 conjugate ; unless they conjugate they go on dividing ; if conjugation 

 does not occur there is more multiplication and senescence. Those 

 which are able to conjugate successfully during the eugamic period 

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

 cycle of development. The period of a cycle depends on the rate of 

 division, and this depends on four factors — the individual temperament 

 of the species, its adaptation to its form of nutrition, the quality and 

 quantity of the food, and the temperature. According to Maupas three 

 conditions are necessary for conjugation — hunger, sexual maturity, and 

 diversity of ancestry of the conjugants. Senescence is marked by de- 

 crease in size, nuclear degeneration, reduction of the mouth-parts and 

 appendages, loss or inhibition of various functions, and sometimes by 

 " morbid sexual hyperesthesia," leading to abnormal and sterile conju- 

 gations between closely related individuals. It ends in death, which 

 Maupas held to be as inevitable for Paramecium as for man. 



The third chapter is devoted to the results of later investigators. 

 As regards the asexual period it seems highly probable that " depression " 

 or " senescence " in Ciliates is due to unhealthy surroundings — un- 

 suitable food, toxins produced by the organisms themselves or by their 

 cultural companions, etc, — and is not due to any inherent inability to 

 live or frustrated necessity to conjugate. Woodruff's conclusion con- 

 cerning Paramecium seems equally applicable to all other Ciliates : 

 " It is probable that most, if not all, normal individuals have, under 

 suitable environmental conditions, unlimited power of reproduction 

 without conjugation or artificial stimulation." 



Popoff tested 11. Hertwig's theory that division is a regulatory 

 reaction to an abnormal mass-relation between nucleus and cytoplasm. 

 He concluded that the " karyoplasmic tension" or instability determines 

 division. Many other investigations bearing on the influence of environ- 

 mental conditions on division are summarized. 



The species of Paramecium consist of an assemblage of distinct races 



Dec. loth. 1916 2 s 



