104 BULLETIN 120, UNITED STATES NATIONAL MUSEUM. 



(unusually clear in this species, fig. 70, &), and others with spindle- 

 shaped anaphase nuclei; dumb-beli nuclei are less common. The 

 macrochromosomes have been counted in a good many of the equa- 

 torial plate and anaphase nuclei and their number found to be 10. 

 (Fig. 70, a and h.) 



All my material of this species from Paludicola hihronii was col- 

 lected at one time from one locality and all the infections show active 

 division, with many daughter cells whose nuclei are in active division, 

 restoring the animals to their binucleated resting condition. The 

 infections from P. hrachyops show the numerous daughter cells with 

 their single nuclei more or less ellipsoidal and in some prophase of 

 mitosis. It is possible a varietal distinction might be made between 

 the Zelleriellas in the two hosts ; but if so, a larger series of infections 

 from both hosts should be studied to see if the conditions are con- 

 stant. The slight distinction observed might better, for the present 

 at least, be treated as a racial divergence. 



ZELLERIELLA PATAGONIENSIS, new species. 



Type. — United States National Museum Cat. No. 16475. 



Host. — Paludicola hufonina (Bell), six good infections from the 

 Straits of Magellan, Patagonia, 1898 ; Hatcher, collector. The type 

 infection is from United States National Museum specimen No. 

 36883. 



Measurements of a mediurri-sized individual. — Length of body, 

 0.152 mm.; width of body, 0.091 mm.; diameter of nucleus, 0.0156 

 mm. ; diameter of endospherule, 0.0016 mm. ; cilia line interval, ante- 

 rior 0.0021 mm., posterior 0.000375 mm. Macrochromosomes ap- 

 parently eight. Larger individuals up to 0.170 mm. are found, these 

 having their nuclei slightly elongated, apparently preparatory to 

 mitosis. 



These Zelleriellas are found in two forms — one wedge-shaped, with 

 usually a short, abrupt, but definite posterior point, not usually 

 sharp; the other very broad and rounded posteriorly. Intergrades 

 between these two extremes are seen. All are very thin. The rest- 

 ing nuclei are nearly spherical. In two uninucleated individuals, 

 dumb-bell-shaped nuclei were studied — one in side view, the other 

 in end view — each showing eight unusually spheroidal macro- 

 chromosomes, short, broad, and thick, instead of ribbon-shaped, as is 

 usual in the Opalinids. This form of the chromosomes, each com- 

 pacted into a sphere, may be the result of abnormal conditions. 

 Possibly the hosts were dead for some time before they were placed 

 in the preserving fluid. The study of the macrochromosomes in liv- 

 ing individuals of other Opalinids has shown them very sensitive to 



