PROTOZOAN FAUNA OF HAY INFUSIONS 263 
given. Of these three, however, air is practically a negligible 
factor in seeding infusions. 
3. In hay infusions, seeded with representative forms of the 
chief groups of Protozoa, there is a definite sequence of appear- 
ance of the dominant types at the surface of the infusion, i.e., 
Monad, Colpoda, Hypotrichida, Paramaecium, Vorticella and 
Amoeba. 
4. The sequence of maximum numbers and of disappearance 
is identical with that of appearance, except that apparently the 
position of Amoeba advances successively from the last (sixth) 
place to the fifth place and then to the fourth place. 
5. A definite sequence of forms is not apparent at the middle 
or bottom of the infusions. 
6. The middle of the infusions is tenanted chiefly by a free- 
swimming population brought there by an overcrowding at the 
top or bottom. 
7. All of the protozoan forms considered (except Amoeba) are 
chiefly surface dwellers and it is evident that when they pass their 
greatest development at the surface this maximum is seldom 
approached again, and their cycle is practically over. | 
8. The major rise and fall in numbers are usually about equally 
rapid, though the final disappearance of an organism may be long 
deferred. 
9. The appearance of any of the protozoan forms under con- 
sideration (excepting Amoeba) in appreciable numbers at- the 
bottom is most often coincident with or immediately subsequent 
to its surface maximum, and portends its more or less rapid elimi- 
nation as an important factor in the life of the infusion. 
10. Numerous abnormal individuals and cysts are frequently 
to be found at the bottom in great abundance immediately after 
the surface maximum. 
11. There is some evidence that amoebae migrate from the sur- 
face to the bottom which is their chief abode. 
12. The observations give the impression that some amoebae 
appear as amoebo-flagellates which gradually increase in size and 
finally assume the form of typical A. proteus. 
