46 BULLETIN 120, UNITED STATES NATIONAL MUSEUM. 



abruptly, giving the posterior end of the body the appearance of a 

 spine-like process such as is found in numerous species (fig. 22, a). 

 The posterior point is rounded, not sharp, at the tip. The posterior 

 end of the body is devoid of cilia. The cilia are long. The ectosarc 

 is rather thick. 



The nuclear condition is different in different individuals, the con- 

 ditions divergent from the mean being shown in a larger propor- 

 tion of the individuals than in most species. Usually there are two 

 independent, ellipsoid nuclei rather near together, the posterior one, 

 usually near the middle of the body (fig. 22, d) . In some individuals 

 the nuclei are further forward (fig. 22, a) , these individuals probably 

 having come from posterior daughter cells at the last transverse 

 division. Numerous individuals are found with dumb-bell-shaped 

 nuclei, having evidently recently come from fission (fig. 22, c). We 

 find all stages between these dumb-bell nuclei and the usual pair of 

 ellipsoidal nuclei. Division of the body occurs when each of the 

 two nuclei are much elongated or are dumb-bell-shaped (fig. 22, e, 

 a daughter cell). One evidently abnormal individual was found 

 which had three greatly constricted, slender dumb-bell nuclei. 



The histological condition of the nuclei is not such as to allow de- 

 tailed study. The number of macrochromosomes seems to be four 

 or eight. Many nuclei show four chromatin masses, others show 

 eight. One can not be quite sure from the preparations that the 

 larger number of chromatin masses, in the latter nuclei, is due to 

 fragmentation of four chromosomes during the metaphase of mi- 

 tosis, as is often seen in other species and as is probable in this 

 species. 



Protooimlina rmtti resembles in shape P. caudata form attenuata^ 

 but in the former species the nuclei are not placed so far forward in 

 the body, the nuclear conditions are more various, or rather the 

 proportion of individuals with nuclei divergent from the mean is 

 greater, and the average nuclear condition is not the same, the nuclei 

 being ellipsoidal and not pointed at one end, also the cilia are longer, 

 while the macrochromosome number appears not to be six. This 

 species is not identical with P. orientalis, which has eight macro- 

 chromosomes, for in the latter species the body is less tapering pos- 

 teriorly. Awerinzew's P. immordialis , from the same species of 

 host and the same general geographic region, is not sufficiently de- 

 scribed for identification, but it can not be P. nutti^ for Awerinzew 

 said each individual in his material had but one nucleus, this being 

 dumb-bell-shaped. 



In the same individual host (United States National Museum No. 

 il438), along with the slender Protoopalinas described, are a number 

 of huge individuals a little longer than the slender ones and three ■ 



