PROTOZOAN FAUNA OF HAY INFUSIONS Zou 
600 per cc. on the 43rd day, and 60 per cc. on the 49th day. 
Approximately this number persisted until the end of the ob- 
servations on the 76th day. 
CIV group. Colpoda developed in greater abundance in this 
group than in any other, attaining, comparatively gradually, a 
maximum of 25,000 per ec. on the 32nd day, falling to 15,000 on 
the 37th day, and to 100 per ce. by the 44th day, and practically 
reaching extinction by the 56th day. 
An analysis of the above data in regard to Colpoda shows that 
this form is adjusted to those surface conditions of infusions which 
exist when the monads have about run their course. 
3. Hypotrichida 
Al group. Representatives of the hypotrichida were the third 
to appear in considerable number and their maximum of about 
2400 per cc. was attained on the 51st day after along gradual rise. 
Their decrease in number was somewhat more abrupt, resulting 
in their extinction by the 85th day of the life of the infusions. 
A II group. These forms were the second to appear and the 
third to reach a maximum growth. This was attained on the 
39th day after a long gradual increase. A rapid decline reduced 
them to about 40 per cc. on the 49th day, and they persisted 
in this number to the 74th day. There was a slight increase in 
number on the 75th day, at which time the observations were dis- 
continued. 
A III group. <A few hypotrichida appeared on the 6th day, 
gradually increased until there were about 400 per cc. on the 15th 
and 16th days, then declined to the 24th day. Their maximum 
of 700 per cc. was reached on the 29th day, after which they de- 
clined until, on the 43rd, they became extinct. 
A IV group. The maximum consisting of 1600 per cc. fol- 
lowed those of the monads and Colpoda and occurred on the 26th 
day. A continuous decline brought the number down to 100 per 
ee. by the 48rd day; and this number persisted to the 50th day, 
