5P0 Janet W. Ran : 



(3) Species with many nuclei, body flattened. 

 To these we may now add — 



(4) Species with two nuclei, body flattened. The nuclei 

 measure 20 yu, across, and are circular in outline, and placed 

 obliquely behind each other. The chromatin material is scat- 

 tered about in masses and is not arranged in any definite 

 order. There is no differentiation into ectosarc and endosarc 

 visible from a general surface view, and the protoplasm appears 

 vacuolated. During movement the posterior portion of the 

 body shows a rigid or rucked appearance as indicated in. 

 Fig. 9, so that it seems to be contracted towards this end, 

 and in this way it moves along. 



Opalina hylarum, n. sp. 



Occurs in HyJa aurea only, and is distinguished from all the 

 other binucleated forms which are circular in cross section by 

 its enormous size. It measures on an average about 420 /x, 

 but some individuals measuring as much as 572 p. have been 

 met with. The average breadth Ts 70 /x. The body is elon- 

 gately oval with a rounded anterior end and a slightly rounded 

 posterior extremity, i.e., it does not taper to a point posteriorly. 

 The protoplasm is granular, and ectosarc and endosarc are 

 clearly distinguishable right to the posterior end. A very well- 

 marked feature of this species is the position of the nuclei, 

 for they are placed very far apart, the hinder one being in the 

 posterior half of the body. (Fig. 10. j The chromatin mate- 

 rial is gathered into masses arranged around the periphery of 

 the nucleus. This is well shown in the transverse section re- 

 presented in Fig. 11. The body is ciliated round its entire 

 surface, the cilia at the anterior end being slightly larger than 

 those towards the posterior end, but there is no posterior 

 portion devoid of cilia (Fig. 15). 



Some individuals showed only a single nucleus, in ditferent 

 stages of division, l)ut these are the results of recent longi- 

 tudinal division. In Figs. 12 to 14 the outlines of three 

 specimens are shown with the positions of the nuclei indicated. 

 In Figs. 12 and 13 the dauoliter nuclei have not yet separated. 



