232 On the Class'ijicatwn of Ciliate Infusoria. 



A rather aberrant group falling under the same head are the 

 Ophryoscolecida3, with their retractile peristome. 



After removing these forms the Oligotricha, /. e. mainly 

 the Tintinnidina, make a more uniform small group, charac- 

 terized by the circular uninterrupted zone bearing cilia of a 

 different form and type, inside of whicli the mouth is 

 situated. 



The Gymnostomata have been made by Biitschli a group 

 of highest order, equal in value with all the other groups 

 combined. It has been shown above that in a number of 

 essential features they differ from the Peritricha and are in 

 harmony with the other Planotricha, and they are especially 

 so with the Aspirotricha. Yet the formation of the mouth, 

 together with some other characters, is so significant that it 

 does not seem natural to reunite these two groups into the old 

 order Holotrichida, as the French authors have done {loc. cit. 

 pp. 430, 452). In the great diversity of the formation of the 

 body among the Gymnostomata we have an interesting 

 analogue with an equally wide range among the Zonotricha. 



The higliest position must be assigned the Oxytrichidge and 

 Euplotida3. Here the differentiation of the main feature of 

 the ciliates, the cilia, reaches its maximum, not only morpho- 

 logically, but also physiologically, combined with the highest 

 development of intellectual faculties, as far as we dare speak 

 of such. In all these points the Peritricha, which have often 

 been placed at the liead of the class, are inferior; and their 

 inferiority is demonstrated also by the fact that at least half 

 of them are epizoa, or commensals ; a large number of animals 

 of both categories live in colonies, either actually coherent or 

 close together, modes of life which are not so much different 

 as is commonly supposed. 



The groups Peritricha *, Gymnostomata, Aspirotricha, 

 Oligotricha, and Zonotricha seem to have the significance of 

 orders of about equal standing with " orders " throughout 

 the animal kingdom. Thus we would have the following- 

 table : — 



Subclasses. Superorders. Orders. 



i Peritricha. Peritricha. 



I Gymnostomata. Gymnostomata. 



Paiitotricha. < 1 Aspirotricha. 



I Trichostomata (em.). -(Oligotricha (em.). 

 [ Zonotricha. 



The Ciliata are here regarded as a class. To this point a 



* The Peritricha might probably be divided into two orders; but, 

 since I have not seen Ltmophora and Kentrochona, the question is left 

 open here. 



