THE OPALINID CILIATE INFUSORIANS. 27 



conditions of cilia arrangement different from that in ordinary in- 

 di\ iduals. Very well-nourished individuals may have the body some- 

 what distended and the lines of cilia will be further apart. Con- 

 versely, starved individuals may be shrunken with narrow intervals 

 between the lines of cilia. 



/. Individuals of different si:)ecies may occur in the same indi- 

 vidual host, and similarly we may have a double or multiple infec- 

 tion by two or more divergent strains of what might well be called 

 one species. 



It is well-nigh impossible in some instances to be sure in his com- 

 parisons that one has selected individuals which are in truly com- 

 parable physiological states and in similar stages in the life cycle. 

 It would be a task of great magnitude and extreme difficulty to de- 

 scribe with any completeness and with discrimination the phenomena 

 as they exist, and when such description had been given the deter- 

 mination of taxonomic divisions would doubtless still have to be 

 artificial in numerous instances. All that will be attempted in the 

 present paper will be to give an intelligible description of the chief 

 data and to adopt the most plausible specific demarcations, but with 

 the decided feeling that further study of wider data will necessitate 

 modification of the present statement. A large part of the material 

 studied was taken from preserved Anura and in some instances the 

 parasites were poorly preserved. It is, however, surprising to see 

 how usable such preserved material usually is. In general, it stains 

 well, and often nuclear structure is well brought out, the chromosome 

 number being readily determined. In numerous instances the ma- 

 terial available is insufficient for as wide comparisons as would be 

 desirable. In some cases only a single infection was found. All 

 one can do is to describe the data found and recognize its limitations 

 and the consequent tentative nature of some of the conclusions ex- 

 pressed. 



In this study are included only the genera Protooyalina^ Zelleriella^ 

 ('epedea.; and Opalina. I believe the family Opalinidae should be re- 

 stricted to these genera and not be stretched to include the very dis 

 similar and evidently not closely related astomatous genera such as 

 Discophrya^ II oflitophrya^ AnoplopKrya^ and others which have often 

 been placed in this family. They are all forms with well differentiated 

 macronuclei and micronuclei,^^ and clearly do not belong in the 

 same family with Protoopalina^ Zelleriella^ Cepedea^ and Opalina, 

 in which there is no such divergent differentiation of nuclei. The 

 differentiation of the nuclei in the Euciliata into maci'onucleus and 

 micronucleus is almost, if not quite, the most remarkable morphologi- 



" The micronucleus of Discophrya has not been demonstrated, but the characteristic 

 macronuclcus of tbe Euciliata is present and probably a micronucleus is present. At 

 any rate Discophrya is nearer to tbe Euciliata than to the Opalinidae. 



