. Biology . ls, as, for example,Euglena and its allies, which may make their food by the plantmethod. We are ignorant of the finer processes of assimilation in Chilo-monas but are justified in assuming that it differs in no essentialrespect from the processes in Amoeba, after the protein foodmaterials are dissolved. As there are no solids the cell containsno undigested food matters, and there is no defecation. Urea,however, is undoubtedly formed since the organism is con-stantly doing work, and this is probably excreted by meansof the contractile vacuole, although it may also pass out by exos-
. Biology . ls, as, for example,Euglena and its allies, which may make their food by the plantmethod. We are ignorant of the finer processes of assimilation in Chilo-monas but are justified in assuming that it differs in no essentialrespect from the processes in Amoeba, after the protein foodmaterials are dissolved. As there are no solids the cell containsno undigested food matters, and there is no defecation. Urea,however, is undoubtedly formed since the organism is con-stantly doing work, and this is probably excreted by meansof the contractile vacuole, although it may also pass out by exos- 56 ORGANISMS OF ONE CELL mosis, as must be the case in many protozoa in which nocontractile vacuole can be found. Chilomonas may frequently be seen in pairs swimmingalong side by side; these are sister cells not yet fully dividedand they have originated by the longitudinal division of thecell. Reproduction thus is of the simplest type, the nucleusalways dividing first, then the cell body, while new fiagella. Fig. 2 2.—A flagellated protozoon, Copromonas siibtilis. A, A normal adult cellbefore division; B, two individuals in conjugation; C, D, E, and F, later stages inthe fusion of cells and nuclei, and formation of protective cyst. (From Dobell.) are formed as outgrowths. It is not known how these originatein Chilomonas but from analogy with other forms of flagellateswhere the process is known, two of the four at least must benew growths; in some cases the old flagella are withdrawn andnew ones are formed; in other cases one of the two flagella goesto each daughter cell. FLAGELLATED PROTOZOA 57 The processes of feeding, growing and dividing continue fordays before other activities occur. Indeed for Chilomonas sofar as known they may continue indefinitely, but from analogywith other forms of Mastigophora where the full life history isknown, these ordinary vegetative processes are sooner or laterreplaced by processes involving a simple kind of fertilizationor sexual union. In
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