Schaudinn has discovered and worked out true syngamic processes, some bisexual, some exogamous, in several other Rhizopods. In _Chlamydophrys stercorea_ the pairing-cells are equal, and are formed by the aggregation of the chromidia into minute nuclei around which the greater part of the cytoplasm aggregates, while the old nucleus (with a little cytoplasm) is lost. These brood-cells are 2-flagellate pairing-cells, which are exogamous: the zygote is a brown cyst; if this be swallowed by a mammal, the original _Chlamydophrys_ appears in its faeces.[72] _Centropyxis aculeata_, a species very common in mud or moss, allied to _Difflugia_, also forms a brood by aggregation around nuclei derived from chromidia. The brood-cells are amoeboid, and secrete hemispherical shells like those of _Arcella_; some first divide into four smaller ones, before secreting the shell. Pairing takes place between the large and the small forms; and the zygote encysts. Weeks or months afterwards the cyst opens and its contents creep out as a minute _Centropyxis_. Finally, _Amoeba coli_ produces its zygote in a way recalling that of _Actinosphaerium_ (pp. 73-75, Fig. 21): the cell encysts; its nucleus divides, and each daughter divides again into two, which fuse reciprocally. Thus the cyst contains two zygote nuclei. After a time each of these divides twice, so that the mature cyst contains eight nuclei. Probably when swallowed by another animal they liberate a brood of eight young amoebae. Thus in different members of this group we have exogamy, both equal and bisexual, and endogamy. Most of the Rhizopoda live among filamentous Algae in pools, ponds, and in shallow seas, etc.; some are "sapropelic" or mud-dwellers (many species of _Amoeba_, _Pelomyxa_, _Difflugia_, etc.), others frequent the roots of mosses. _Amoeba coli_ is often found as a harmless denizen of the large intestine of man. _Amoeba histolytica_, lately distinguished therefrom by Schaudinn, is the cause of tropical dysentery. It multiplies enormously in the gut, and is found extending into the tissues, and making its way into the abscesses that so frequently supervene in the liver and other organs. _Chlamydophrys stercorea_ is found in the {58}faeces of several mammals. The best monograph of this group is that of Penard.[73] 2. FORAMINIFERA[74]