THE OPALIXID CIIJATK IXirsoUIANS. 265 



Chromosome nvmher^ especially the number of the readily ob- 

 served macrochromosomes. is a most usable diaf^nostic character iii 

 the two binuoleated <,^enera. In the multinucleated species tiie nuclei 

 are small and the chromosomes numerous, so it is difficult to deter- 

 mine the chromosome number. 



From this revieAv of the usable specific diafrnostic characters it 

 is seen that the}- are rather numerous and that they will irive a large 

 number of combinations of characters. Most species, in consequence, 

 are fairly clearly distintruished. In some instances, however, the 

 taxonomic problem is hopeless, at least to one having but few infec- 

 tions of each species. 



In section 7 of this paper, in connection with problems of 

 zoogeography, subgeneric groups of species within the genera Pro- 

 toofdlma, Cepedea^ and Opalina are discussed. 



6. THE RELATIONSHIPS OP THE OPALINIDAE. 



We have discussed the relationships within the family Opalinidae. 

 NoAv we may consider the relationships of this family to other groups. 

 What is its relation to the Ciliata in general, and especially to the 

 astomatous forms which have often been included among the Opa- 

 linidae? What relationships with lower groups of Protozoa are 

 indicated? If we can find light upon these questions, we may find 

 indications of the source and manner of origin of the true Ciliata, 

 which are in some respects the most remarkable of organisms. Let 

 us compare the Opalinidae with both Flagellata and Euciliata and 

 M-ith respect to a series of characters, form of bo^y, structure of 

 body plasma, pellicle, ectosarc, endosarc, ectosarc spherules, en- 

 dopherules. excretory organs, locomotor organs, kinetic structures, 

 general nuclear condition, trophic chromatin, reproductive chro- 

 matin, manner of asexual reproduction, presexual and sexual phe- 

 nomena, life cycle as a wdiole, mitotic mechanism, occurrence of 

 mitosis and amitosis, binucleate and multinucleate conditions, 

 chromidia. In what of these features do the Opalinidae resemble 

 the Euciliata, with which they have usually been classed, and in 

 what regards do they differ from them? In what respetts do they 

 agree with and differ from the lower Protozoa, the Plasmodroma? 



The Jjochj form is not distinctive. The less modified Opalinids 

 are Euglenalike in shape, so are some Euciliates. The alveolar 

 cytoplasm is not distinctive. 



The pellicle is delicate, thicker than in most Plasmodroma, about 

 as it is in, say, Paramecium: It differs from the pellicle of Plas- 

 modroma in general, and agrees with that of Euciliates in being 

 longitudinally spirally furrowed and in having rows of cilia inserted 

 in some, at least, of these furrows. This is a distinctly Ciliate char- 

 acter. In at least some Opalinids which I have obscrviMl tliore are 

 83103— 2.3 IS 



