THE OPALINID CILIATE INFUSORIANS. 



173 



My infections from Folypedates leucomystax show Opalinids of 

 elongated, slender form, but shorter than typical C. ophis. They 

 are perceptably more densely clothed with cilia. Their nuclei also 

 are larger and are ellipsoidal, instead of spherical as in the latter 

 species. 



These animals show a remarkable series of transverse constric- 

 tions. It seems that many fission furrows have started without com- 

 pletely cutting through, so that the body appears as a series of 

 segments. Some of these constrictions are deeper, some are shallower. 

 It is evident that the first furrows have not been completed before 



Fig. i40. — Cepedea segmentata, X 460 diameters. The nuclei should be shown 



MOKE ELONGATED. 



new ones appear. In other Opalinids, previous to the period of 

 sexual reproduction, we find a frenzy of fission, division furrows ap- 

 pearing so rapidly that a second or third division may be begun be- 

 fore the first is completed. The individual figured is not a very ex- 

 treme example from its infection, but in two other infections no 

 specimens are found with so many pseudometameres. Nearly all 

 individuals, however, except the smallest, in all the infections studied 

 show the " segmentation '' more or less well developed. In section 6 

 of this paper the phenomena of speciation among the Opalinids will 

 be treated in their broader aspects and this species will there be re- 

 garded as the last term in the evolution of the Opalinids so far as 

 the tendency to inhibit and delay division of the body is concerned. 



