140 On the Genefirs of the Ciliate Protozoa 



18. A concrete case may be given in illustration. The life-cycle 

 of Styloiujchia pustulata may be tabvilated thus' : 



Divisions. 

 1 — Excon j ugant. 



: [ Period of immaturity (agamic period). 

 130 — Age of puberty. 

 : • Eugamic period. 

 170 



: [ Period of senescence. 

 316— Death. 

 The length of one complete cycle for this species is thus 316 divisions, 

 but Maupas found that the cycle is of diiferent length in different 

 species. For example, Sti/luni/cliia mi/tili(s died of old age after 319 

 successive bipartitions, O.rytriclni and Urii/chodromus (jrandis after 

 320 — 330, Leucophrys patula after 660. 



19. The period of time occupied by a developmental cycle depends, 

 of course, upon the rate at which division takes place. This, according 

 to Maupas, depends upon four factors : (1) the individual temperament 

 of the species ; (2) the biological adaptation of the species to its form 

 of nutrition; (3) the quality and quantity of the nutrition^ ; (4) the 

 temperature. Light and other external factors he found to have no 

 appreciable effects. 



20. Three conditions are, according to Maupas, necessary for 

 successful conjugation. These are: (1) hunger; (2) sexual maturity; 

 (3) diversity of ancestry of the conjugants ("f^condation crois^e") — that 

 is, the conjugants must nut be related-'. "External physical conditions 

 play no determining part in the appearance of conjugation ^" Hunger — 



' The division at which the eugamic period ends and the period of senescence begins 

 is variously stated by Maupas to be the ICOtli and tlie 170th — 180th. 



- Earher experiments had been made by Balbiani (1860) in this connexion. He states 

 that be placed three individuals of Paramecium aurelia separately in three different watch- 

 glasses. In one of these he placed (i drops of pure water, in another 6 drops of a pepper 

 infusion containing many bacteria and amoebae, in the third 3 c.c. of the same infusion. 

 After 16 days, the first animal had divided once, and both the daughter individuals died. 

 After a similar length of time he found the second animal had jiroduced 17 offspring : 

 whilst the third had produced in 17 days so numerous a progeny that he estimated them 

 at approximately 2100. 



■■I If they are, their union is sterile, or produces weakly progeny which ultimately die. 



■* Biitschli (1887) after analysing all the evidence avadable at the time, had concluded 

 that "external conditions which call forth conjugation have not yet been determined." 



