THE OPALINID CILIATE INFUSORIANS. 195 



Measurements of A^ a large individual, and B, a small individual 

 from this infection are — 



The Opalinae in all these infections considerably resemble O. 

 oMrigonoidea lata, and . ohtrigonoidea orhiculata and seem closely 

 related. 



Ver}- much smaller Opalinae with larger nuclei are seen in a speci- 

 men of the same variety of frog, United States National Museum 

 Xo. 3055J:. 27 mm. long, from Pico Blanco, Costa Rica, W. M. Gabb, 

 collector (fig. 163, c, d, e). A specimen of these Opalinae has been 

 deposited with the United States National Museum as Xo. 16591. 



The measurements of a rather small individual are. — Length of 

 body 0.096 mm. ; width of body 0.0435 mm. ; thickness of body 0.016 

 mm. ; diameter of nucleus 0.005 mm. to 0.0065 mm., mean 0.0052 mm. ; 

 diameter of endospherule 0.0015 mm. ; cilia line interval, anterior 

 0.00222 mm., posterior 0.0045 mm. 



The largest individuals are only 0.117 mm. in length. 



Noting the size of the three hosts mentioned and comparing the 

 respective sizes of their Opalinae, one sees that the smallest (young- 

 est) host has the smallest Opalinas, and the largest (oldest) host 

 has the largest parasites, but the nuclei of the smallest Opalinas are 

 much the largest. Whatever there may be in these conditions more 

 than mere coincidence, we do not understand, for we do not know 

 the details of structure throughout the life history of any multi- 

 nucleated Opalinid. The study of these phenomena in detail would 

 be of much value. Compare Hegner and Hsiang-Fong Wu (1921), 

 published since this paper was ready for press, in which some de- 

 tails of growth are described for 0. \larvarum\. 



OPALIXA. species (?). 



A specimen of this form has been deposited in the United States 

 National Museum as No. 16611. 



Host. — Bufo haematiticus Cope, one infection, from a United 

 States National Museum specimen, one of many in a jar numbered 



