Finally there is the less common type of cyst formation, such as is found in the flagellate _Oicomonas termo_ described by Martin.[19] This flagellate, in common with all other forms, reproduces by dividing into two; the division of the nucleus initiating the process. At certain undetermined periods of the life history, however, conjugation occurs between two similar animals forming a large biflagellate body known as the zygote. After swimming about for varying periods of time, during which the size increases and a large vacuole appears, the zygote secretes a thick wall, loses its flagella, and becomes a cyst. While in this condition the two gamete nuclei fuse to form one, and eventually a single _Oicomonas_ emerges from its cyst. Similarly in _A. diploidea_ the cysts are formed after two individuals have come together. In the young cysts two amœbæ are found in close association, and according to Hartmann and Nägler[12] a sexual process occurs inside the cyst involving a “reductive” division of the nuclei. This requires confirmation, but it is certain that only one individual comes out of the cysts, which originally contained two amœbæ. Such cysts have been termed by some writers “reproductive,” evidently a misleading term, since no increase in numbers, but rather a decrease, results from the process. A better term is, perhaps, conjugation cyst. In soil protozoa, then, three different modes of cyst formation obtain, and failure to make the distinction inevitably leads to confusion. Before leaving the question of life histories, reference must be made to a peculiar and characteristic feature of _Nægleria gruberi_. This amœba under certain circumstances assumes a free-swimming biflagellate stage. After variable periods of time the flagella are lost and the ordinary amœboid condition resumed. What are the factors concerned in the production of flagellates is unknown, but flooding the coverslips with distilled water is an effective method for causing their appearance. DISTRIBUTION OF SOIL PROTOZOA. For both the bacteria and algæ observations have been made regarding their distribution through successive depths of the soil; little can be said, however, about the protozoa in this connection. It is certain that they occur throughout the first six inches of the Rothamsted soils, though their relative frequencies in the successive inches has not been determined, but probably they are most abundant in the 2nd to the 4th inch. In this country experiments have not been made to determine whether sub-soil normally contains protozoa; but from some South African soil, taken under sterile conditions 4 ft. down and examined in this laboratory, large numbers of protozoa were cultivated. This soil, however, could not, for various reasons, be regarded as a typical sub-soil.