426 THE AMERICAN NATURALIST. [VOL XXXII. 
In opposition to the Peritricha, we may give to this second 
group the name Pantotricha. Among the latter, those forms 
having a true adoral zone with a distinct beginning and end 
at the mouth entrance, and bearing transverse rows of single 
cilia, that is, the Hypotricha and most of the Heterotricha, 
evidently are of a common type, and range in one group, which 
I propose to name Zonotricha. True, the extreme forms are 
very different, e.g., a Stentor on the one hand, and a Stylony- 
chia or Euplotes on the other. But it is well known that both 
series, by gradual changes, in fact, run together, and that there 
are forms which may be ranged with one or the other. Many 
Peritricha are quite depressed, while there are Oxytrichidz 
nearly terete, showing little differentiation of the dorsal and 
ventral faces, with fine and densely set cilia over most of the 
body (Strongylidium). And such forms as Stichospira’ make 
the distinction still more illusory. Tactile hairs (or “dorsal 
cilia ”) are wanting in some of the Oxytrichidz as well as in 
Euplotide. and Aspidiscidze. Longitudinal differentiation in 
the ectoplasm of Urostyla, etc., comes very near the myonems 
in Peritricha. With the Zonotricha range Halteria, probably 
also Strombidium and Gyrocoris. A rather aberrant group, 
falling under the same head, are the Ophryoscolecide, with 
their retractile peristome. 
After removing these forms, the Oligotricha, z.e., mainly the 
Tintinnidina, make a more uniform small group, characterized 
by the circular uninterrupted zoye bearing cilia of a different 
form and type, inside of which the mouth is situated. 
The Gymnostomata have been made by Biitschli a group of 
highest order, equal in value with all the other groups com- 
bined. It has been shown above that in a number of essential 
features they differ from the Peritricha and are in harmony 
with the other Pantotricha, 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 Holotri- 
chida, as the French authors have done (oc. cit., pp. 430, 452). 
1 See the writer’s article, this journal, vol. xxxi, No. 366, June, 1897, pp- 
535-541- . 
