113 



down to the daughter cells, as are, for example, the pyrinoids of plant 

 cells. The spherules of the endosarc resemble in size and form the larger 

 chromatin spheres of the nuclei and they react to the same stains, but 

 more faintly. It is possible they are derived from the latter, but I am 

 not yet convinced that this is true. The endosarc spherules are highly 

 refractive in the living animal. They do not stain intra-vitam with any 

 of the usual intra-vitam dyes except neutral red, methyl violet, dahlia 

 and gentian violet. One often finds the spherules of the endosarc 

 showing a dumb-bell form and it is probable that they divide by con- 

 striction. Both in the living animal and in stained preparations they 

 are seen at times to be granular, the more evident granules being peri- 

 pheral while the core is apparently more nearly homogeneous. 



The spherules of the ectosarc are larger, they stain with plasma 

 dyes rather than chromatin dyes and take intra-vitam stains more strongly. 

 In the living 0. iniestinaUs^ 0. caudata and 0. dimidiata, especially in 

 the minute forms found in the spring, they are sometimes yellow. This 

 yellow color is emphasized by acetic-carmine while the endosarc sphe- 

 rules are stained red. 



During the whole year Opalina divides by fission. This is usually 

 longitudinal, but occasionally transverse division is found. The latter 

 is rare in the binucleate forms. During summer, fall and winter these 

 divisions take place very slowly, days being required for the completion 

 of one division. In the spring, as the breeding season of the host ap- 

 proaches, the rate of division increases, and the animals become very 

 minute. They then encyst and pass with the foeces of the host into the 

 water, further development taking place in the rectum of the tadpole. 

 It is not necessary for the cysts to lie in water any time in order to 

 secure good infection. 



Coujugatiou. 



Opalina intestinalis and 0. catidata. 



The infection cysts of these binucleated species are usually uninucle- 

 ated though frequently one finds binucleated cysts. The animals which 

 emerge from the cysts in the small intestine or rectum of the tadpole 

 begin to divide by longitudinal and transverse division, the divisions 

 being rather slow, apparently occupying at the least about one day. 

 After from forty to eighty hours minute tailed gametes are found (fig. 2). 

 Their tails are very sticky, usually they swim with the tail in front. 

 The tailed gametes are of two sizes, one about twice as large as the 

 other, the smaller being formed from the latter by longitudinal division. 

 I have never seen two tailed gametes conjugate as Neresheimer has 

 described. 



