The sequence of the protozoan fauna of hay infusions

1. In hay infusions, seeded with representative forms of the chief groups of Protozoa, there is a definite sequence of appearance of the dominant types at the surface of the infusion, i. e., Monad, Colpoda, Hypotrichida, Paramœcium, Vorticella and Amœba.

2. The sequence of maximum numbers and of disappearance is identical with that of appearance, except that apparently the position of Amœba advances successively from the last (sixth) place to the fifth place and then to the fourth place.

3. A definite sequence of forms is not apparent at the middle or bottom of the infusions.

4. The middle of the infusions is tenanted chiefly by a freeswimming population brought there by an overcrowding at the top or bottom.

5. All of the protozoan forms considered (except Amœba) 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.

6. The major rise and fall in numbers at the surface are usually about equally rapid, though the final disappearance of an organism may be long deferred.

7. The appearance of any of the protozoan forms under consideration, excepting Ameba, 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 elimination as an important factor in the life of the infusion.

8. Numerous abnormal individuals and cysts are frequently to be found at the bottom in great abundance immediately after the surface maximum.

9. Emphasis is put upon the strictly biological interrelations (e.g., those involving food and specific excretion products) of the various forms as the most important determining factors in the observed sequence.