20 



BULLETIN 120, UNITED STATES NATIONAL MUSEUM. 



slieimer describes certain cysts with sj)iiidle-shaped nuclei found in the 

 tadpole. These he regards as encysted zygotes. I have not ob- 

 served them, nor has Brumpt (1915) been able to find them. Their 

 further fate has not been followed. The zygotes thus formed in the 

 recta of the tadpoles resemble the full-grown Opalinids, except for 

 size and the fact that they have bat a single nucleus. The details of 

 development into full-sized Opalinids have not been followed. 

 Growth and multiplication occur during the first month much as they 

 do among the larger forms, Brumpt (1915) has found that after 

 some weeks the Opalinids in the recta of the tadpoles show an epi- 

 demic of division followed by encystment, the cysts being infection 

 cysts identical structurally with those in the adult hosts in the spring 

 of the year. This process continues the abundance of the cysts in 

 the pools and renders more certain the infection of the tadpoles 



Fig. 8. 



-Protoopalina intbstinalis ; fohmatiox or the copula nucleus. 



DIAMETEUS. 



X 673 



which develop from the eggs that are laid late. The chief points of 

 interest unobserved as yet are two. First is the exact manner of re- 

 establishing the binucleated condition. As the Opalinids have not 

 been successfully reared outside the host, and as many of the phe- 

 nomena, especially those of fission, are distorted in cultures, it is not 

 easy to learn in just what way binucleation is reestablished. It is, of 

 course, easy to imagine, but we do not know the exact facts. The 

 second undetermined point is the manner of reestablishing the double 

 character of the chromatin, with a set of macrochromosomes and a 

 distinct set of microchromosomes. This last point in question will be 

 more clearly indicated after reading the description of the expulsion 

 of chromatin from the nuclei at about the time of encystment. (See 

 p. 22.) 



But the details of the sexual phenomena should be described. The 

 subject needs further study, for there are certain discrepancies! be- 



