VI 



CILIATA 



149 



mytihis the produce of a being after conjugation died of senility 

 after 336 fissions; in Leucophrys after 660. 



Save in the Peritrichaceae (p. 151) conjugation takes place 

 between similar mates, either of the general character and size of 

 the species, or reduced by fissions, in rapid succession, induced by the 

 same conditions as those of mating. The two mates approach, lying 

 parallel and with their oral faces or their sides (Stentor) together, 



A A 



/* 2 /* 2 fi a ^ 



A A 



fi M 



Z Z r 



M H 



Z, Z, 



A A 



z, z z. 



M 



M /i 



Fig. 53. Diagram of conjugation in Colpidium colpoda. Horizontal line means degenera- 

 tion ; parallel vertical lines, separation of gametes ; broken lines (above), boundary 

 between pairing animals ; (below), first fission ; single vertical line, continuity or 

 enlargement. M, Meganucleus ; fi, micronucleus ; Z, zygote-nucleus. 



and partially fuse thereby ; though no passage of cytoplasm is 

 seen it is probable that there is some interchange or mixture. 1 



The meganucleus lengthens, becomes irregularly constricted, 

 and breaks up into fragments, which are ultimately extruded or 

 partially digested. The micronucleus enlarges (Fig. 5 2, A) and 



conditions ; and that minute doses of beef-tea or various mineral salts will not 

 only keep up the higher rate, but even stave off senescence. Minute doses of 

 alcoho 1 ,vill keep up the higher rate, but not avert senescence. He considers that 

 Maupas' generalisations are in most respects too sweeping (Arch. Entw. xv. 1902, 

 p. 139). But Dr. James Y. Simpson informs me that the possibility of stimulative 

 regeneration has been found to be limited. See also Calkins and Lieb, Arch.'Prot. 

 i. 1902, p. 355. 



1 As inferred by Hickson from the prolongation of the union. 



