200 COMPARATIVE ANATOMY 



transverse division at the normal rate of two or three divisions 

 in the twenty-four hours. 



The course of conjugation is in all essentials the same in the 

 other members of the genus Paramecium as in P. caudatum, 

 but the details are slightly different. In P. aurelia the process 

 is complicated by the presence of two micronuclei. In P. 

 bursaria the final stages are somewhat simplified, and resemble 



raraTneciu-TTv' caudotuTrv 



(_!/oL]oicLi,v-T'T' coliaoAa 



Fig- 43- 



Diagrams of the course of conjugation in the two infusoria Paramecium caudatum and 

 Colpidium colpoaa. The transverse lines represent the different stages into which 

 the process may be divided. The black circles represent persistent nuclei, the 

 empty circles stand for those which disintegrate and disappear. The division of the 

 gametes are represented by the ovals enclosing the nuclei at the top of the figure. 

 (After Maupas.) 



those of Colpidium colpoda, a ciliate infusorian whose conjuga- 

 tion is represented in the diagram (fig. 43) for comparison. It 

 will be observed that the behaviour of the micronucleus up to 

 stage G^ is identical with that of P. caudatum, but that four 

 daughter nuclei are formed from each combination nucleus 

 instead of eight, and at the first division two of these become 

 the macronuclei and two the micronuclei of the daughter forms. 

 In P. bursaria the original macronucleus does not break up 



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