184 BULLETIN 120, UNITED STATES NATIONAL MUSEUM. 



Fig. 151. — Opalina obtrigonoidea, from Rana pipiens, optical section showing the 

 bxcbbtorr pore and the "bladder" of the excretory canal, x 1,000 dia.mbters. 

 Tub two nuclei apparently lying in the "bladder" are in reality above it. 



Fio. 152. — Opalina obtrigonoidea, from itvNA palustbis, x 117 diameters. 



J 



I 



Fio. 153. — Opalina obtbigonoidea, fbom Rana palustbis, sample individuals fbom 

 another host, X 117 diameters. 



