634 0. CLIFFORD DOBELL. 



Neresheimer has accurately, though briefly, described this 

 phase, aud I have been able to confirm fully his observations. 

 In the spring-, at the frog's breeding season, Opalina 

 encysts, and is cast out into the water in the excreta. The 

 changes which take place before encystation are as follows : — 

 The adult animal divides in an oblique manner, giving rise to 

 two daughter individuals. Each of these then divides into 

 two, and these again divide until small Opalinse containing 

 several nuclei are formed. During these divisions important 

 changes occur in the nuclear apparatus. The nuclei are seen 

 to become less distinct, this being due to the fact that the 

 chromatin is cast out into the cytoplasm in the form of small 

 strands and particles, or chromidia. Sometimes I have 

 observed these united to form a network thi'ough the 

 creature. Finally, the original nuclei vanish, and we are left 

 with only distributed chromatic material. The chromidia 

 soon become aggregated at certain centres, and thus synthe- 

 sise new nuclei, which are from two to ten in number. 

 These nuclei are seen to be composed of large chromatin 

 granules, arranged irregularly. They chauge, however, with 

 the approaching encystment of the animal, which soon takes 

 place. The chromatin travels to the periphery of the nucleus 

 where it becomes arranged in a thin layer with two to four 

 large cap-like thickenings.^ In optical section these nuclei 

 appear as rings. The cap-like projections are soon cast off 

 into the cytoplasm, where they degenerate, this constituting 

 the first nuclear reduction. Encystment follows, and in the 

 normal course of events the cyst is cast into the water, where 

 a second reduction of chromatin occurs. I will leave the 

 description of the life-cycle at this point, merely noting that 

 each nucleus is now a reduced gamete nucleus, and takes part 

 in the formation of a single ciliated gamete whose destiny is 

 to conjugate in the tadpole's gut. The essential points in the 

 process just described are (1) formation of chromidia, 

 (2) synthesis of fresh nuclei from these chromidia, (3) reduc- 

 tion of chromatin, and (4) encystment. 



' First described by Locwcntlial as " niicrotiucleus-like structures." 



