62 



BULLETIN 120, UNITED STATES NATIONAL MUSEUM. 



The specimens of Xenopus were all preserved in formalin and in 

 consequence the Opalinids are not in good condition for detailed 

 study. The lines of insertion of the cilia can hardly be seen, and the 

 endospherules can hardly be measured. The details of nuclear struc- 

 ture are not so clear as to allow determining with confidence the 

 number of the chromosomes, but the general nuclear condition can 

 be observed. 



This Protoopalina belongs to the group of species which have the 

 posterior end of the body prolonged into a tapering, slender, pointed 

 process, a group of species including P. diflocarya from Chile, 

 and P. acuta and P. papuensis from Australasia, and should have 

 been described in connection with them. The considerable resem- 



Pio. 36. — Protoopalina xbnopodos, x 460 diameters 



TELOPHASE OF MITOSIS. 



SHOWS NUCLEI IN AN EARLY 



blance to P. africana led to describing it here, but the other arrange- 

 ment would perhaps be better. 



In the usual mitotic condition of its nuclei Protoopalina xenopodos 

 differs from all the other pointed species of the genus. Exceptional 

 individuals, with nuclei in active division (fig. 36, c) , show chromatin 

 masses (apparently eight in number ?) in place upon the spindle. 

 The ordinary nuclei, not in active mitosis, show the same (eight ?) 

 distinct chromatin masses, but not in any definite arrangement. 

 These nuclei, in the usual condition, are elongated in the axis of the 

 body, being either ellipsoid, or frequently somewhat pear-shaped. 

 The two nuclei are found to be connected by a thread in case the con- 

 dition of the specimen is favorable for observation. Probably they 



