30 BULLETIN 120, UNITED STATES NATIONAL MUSEU^I. 



though this may be due only to the fact that in many species studied 

 the preservation of the nuclei was not such as to allow clear analysis 

 of the nuclear structure. 



This departure in the Profoopalininae^ and to a far less degree in 

 the Opalininae, from the nuclear condition found in other animals 

 and plants is most remarkable. In no other living things, so far as 

 I know, do nuclei which have entered upon mitosis characteristically 

 come to rest before they have completed the mitosis. This phenome- 

 non was first observed in Protoopalina [" Opalina^^] mitotica (Met- 

 calf, 1912) and was later seen by Awerinzew (1913) in his Proto- 

 opalina [" Opalina "] primordialis. The present studies show its 

 prevalence throughout this genus and also among the Zelleriellas. 

 These mitotic phenomena give one important indication of the rela- 

 tionships between species. In a subsequent section of this paper the 

 light these phenomena throw upon the question of the origin of the 

 Ciliata and of the remarkable nuclear conditions in the Euciliata, 

 will be discussed. 



The several species of Opalinidae will first be described and I will 

 then attempt a summary description of the genera, subgenera, and 

 subfamilies. 



A word of explanation as to the figures should be noted. Magnifi- 

 cations of 117, 460, 1,000, and 2,000 diameters are most used, and 

 magnifications should be noted before comparing drawings. Many 

 figures give merely the outlines of the body. Generally such figures 

 show a number of drawings indicating the range of shape and size in 

 the infection. Other figures add outlines of the nuclei, some includ- 

 ing the macrochromatin masses. Cilia are in no case accurately 

 drawn. They could not be except in highly magnified drawings, and 

 then only in those cases in which fresh material has been available 

 for study. In most instances the drawings do not indicate the fact 

 that the cilia are more crowded over the anterior portion of the body. 

 In the more detailed drawings the endospherules are in solid black 

 while the ectospherules usually are not shown. In many of the figures 

 the limits of the morphologically anterior end of tlie body are marked 

 by two dots placed outside the contour of the body or its cilia. 



Genus PROTOOPALINA. 



Cylindrical or spindle-shaped Protoopalhiinae^ circular, or nearly 

 so, in cross section. 



PROTOOPALINA PRIMORDIALIS (Awerinzew). 



Opalina primordialis Awerinzew (1913). 



Host. — Rana nutti Boulenger. 



These Protoopalinae were found along with Nyctotherus in a sin- 

 gle specimen of this frog fom Amani, German East Africa. Awerin- 



