RHIZOPODA 5 7 



larger prey. Temporary encystment in a " hypnocyst " is not 

 infrequent in both naked and shelled species, and enables them 

 to tide over drought and other unfavourable conditions. 



Schaudinn has discovered and worked out true syngamic 

 processes, some bisexual, some exogamous, in several other Ehizo- 

 pods. 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 aggre- 

 gates, while the old nucleus (with a little cytoplasm) is lost. 

 These brood-cells are 2 -flagellate pairing -cells, which aie 

 exogamous : the zygote is a brown cyst ; if this be swallowed by 

 a mammal, the original Chlamydophrys appears in its faeces.^ 



Centropyxis aculeata, a species very common in mud or moss, 

 allied to Bifflugia, 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 Ehizopoda live among filamentous Algae in 

 pools, ponds, and in shallow seas, etc. ; some are " sapropelic " or 

 mud-dwellers (many species of Amoeba, Pelomyxa, Bifflugia, 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 Schau- 

 dinn, 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 



' Arb. Kais. Gesundheiisamte Berlin, xix. 1903. 



