TilK OPALlXll) CILIATE INrUS.yRIAX;?. 253 



after the nucleus has divided, the division of the body is still ilelayed, 

 this delay in the division of the body being the thing that causes 

 the binucleated and multinucleated conditions. In ProtoopaUna 

 and Zelhriella^ which are characteristically binucleated, the nuclei 

 have already divided into two, but the corresponding division of the 

 body does not occur. It dt)es, however, occur in time. When the 

 two nuclei again enter upon mitosis, the delayed division of the body 

 takes place, so that, except in two species, not more than two distinct 

 nuclei are found in the one body. 



Different species ditfer as to the exact mitotic condition in which 

 the nuclei will be found at the time when division of the body 

 occurs. In some species, as for example /^ mturiuilh (Hg. ;i7. j). G4) 

 or /\ stevensoni (fig. 2G, p. 51), the two nuclei are ellipsoidal at the 

 time of division of the body. In P. saturnalis each nucleus is at this 

 time in a diffuse reticulate condition. In other species, as /''. caiidata 

 (fig. 19, p. \'l) and P. 'nttestlnaJ'/s (fig. 27. p. 52). each nucleus is in 

 an elongated ellipsoidal anaphase Avhen the body divides." In P. 

 reguldris (fig. 41, p. 70) each nucleus is in a slender si)in(lle-shaped 

 anaphase. In P. pelohatld'iH (fig. IG. p. 89) each nucleus is in a dumb- 

 l)ell-shaped anaphase; so also in P. Jjufonis (fig. 45. p. 74). In P. 

 acaplviopodos (fig. 4G. p. 7G) and P. niitottca (fig. 48. p. 7S) both luiclei 

 are in a dumb-bell-shaped early metaphase before the body divides. 

 In P. inexkana (fig. 49. ]>. 79) division of the body does not occur 

 until each nucleus has reached a dumb bell-shaped late metaj)hase 

 condition. In P. foDtiosae (fig. 50, p. 81) the fission occurs only after 

 wich of the two nuclei has given rise to two almost distinct daughter 

 nuclei connected only by a slender thread of considerable length. In 

 P. qu(i(lrinucleata (fig. 51, p. 82) the two nuclei have completely 

 divided into four, and division of the body does not take place until 

 each of these four nuclei has entered upon the next mitosis. In P. 

 wconaclenta (figs. 52 and 58, pp. 88 and 84) as many as 10, possibly 

 in some cases more, nuclei may be present before division of the 

 l;ody occurs. 



A somewhat similar, but less extensive series could be given for 

 the species of Zellerlelld. Z. demirobatidh (figs. C3 and 64, p. 9G) 

 may divide while the two nuclei are spherical, or only a little 

 elongated, while, at the other extreme, Z. \^engystomopsis\ (fig, G2, 

 p. 95) does not divide until each nucleus has completely divided into 

 two, so that there are four distinct nuclei in the body. Between these 

 two extremes are numerous forms, as Z. palad'tcolm (fig. 70, p. 108) 

 and Z. darwinii (fig. 74, p. 108). which divide while the two nuclei 

 are spindle shaped. Z. afelopi/.i-ena (fig. 59, p. 92) and Z. hylaxena 

 (fig. 78, p. 112), which divide while the two nuclei are dumb-bell- 

 shaped, and Z. antilUensk (fig. 84, p. 118). which divides while the 

 two daughter nuclei of each pair arc connected merely l)y a thread. 



