116 BULLETIN 120, UNITED STATES NATIONAL MUSEUM. 



animal turns over and presents itself edge on, it is seen to be very thin as 

 compared with its breadth [fig. 81, c], and in section would appear flat or oval. 

 Metcalf [1909] divides Opalinae into the following groups: 



(1) Species with two nuclei, bodies circular in cross section. 



(2) Species with many nuclei, body circular or broadly oval in cross section. 



(3) Species with many nuclei, body flattened. 

 To these we may now add 



(4) Species with two nuclei, body flattened. The nuclei measure 20m 

 across, and are circular in outline, and placed obliquely behind each other. 

 The chromatin material is scattered 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 ridged or rucked 

 appearance as indicated in figure 81, b, so that it seems to be contracted towards 

 this end, and in this way it moves along. 



Fig. 81. — Zelleriella binucleata. (After Rafb*.) Thei heavy lines in 6 (shaded 

 IN Raff's drawing) represent "ribs"; o is an edge view. 



Measurements of an ordinary individual, — Length of body, 0.157 

 mm. ; width of body. 0.1 mm. ; diameter of nucleus, 0.02 mm. 



This species resembles in body form Z. paludicolae from Paludi- 

 cola hTachyops and P. Mhronii, but has a more definite, though 

 slight, posterior point. Its nuclei are doubtless seldom in mitosis 

 or Raff would have described their appearance during this phase. 

 The resting nuclei are considerably larger than in Z. paludicolae. 

 It is in all likelihood a distinct species, though study of the mitosis 

 would be desirable before definitel}' determining this point. Z. hi- 

 nucleata closely resembles in body from the shorter and broader 

 daughter cells of Z. hrasiliensis from Leptodactylus ocellatus., but 

 in the latter species the nuclei are ellipsoidal in the resting condition. 



THE ZELLERIELLAS OF THE BUFONIDAE. 



The Zellerriellas found in the Bufonidae are peculiarly difficult 

 to distinguish in some cases. We will first note the two species 

 which have previously been described and will then pass to the 

 numerous forms in my present material. 



