236 BIOLOGY OF THE PROTOZOA 



the flagellates, usually about eight in number, within the host cell 

 (Fig. 122, 12). The products of this method of multiplication are 

 full-sized trypanosomes, complete in their structure, and differing 

 but slightly in their characters from those found in the blood of the 

 rat. They escape from the host-cell into the lumen of the stomach." 

 (loc. cit., p. 290). 



Similar multiple division phases have been described for Trypano- 

 soma cruzi (Chagas, Hartmann), for Eutrichomastix seryentis, and 

 Tetratrichomonas prowazeki (Kofoid and Swezy), Lophomonas blattae 

 (Janicki) and others. In these cases, as in Trypanosoma lewisi, the 

 number of individuals formed is usually eight. 



In Sarcodina there is a typical alternation of generations combined 

 with multiple division best illustrated in the Foraminifera. Accord- 

 ing to the independent observations of Schaudinn (1903) and Lister 

 (1905) the zygote develops into an agamont characterized by an 

 initial central chamber of relatively minute size (microspheric shell, 

 Fig. 123, B). When fully grown the chromidia-laden protoplasm 

 breaks up by multiple division into a great number of ameboid 

 agametes (pseudopodiospores) each with a number of chromidial 

 granules which fuse to form a nucleus. Each agamete develops 

 into a gamont or individual of the sexual phase, characterized by a 

 large initial central shell-chamber (macrospheric shell, Fig. 123, 

 D, E). When these gamonts are mature, they also break up by 

 multiple division into myriads of flagellated gametes (flagellispores, 

 F). These are isogametes which fuse two-by-two forming zygotes, 

 and these zygotes repeat the cycle by developing into microspheric 

 individuals (Fig. 123, A). Similarly in Arcella vulgaris there is an 

 alternation of generations which is even more complicated than that 

 of the Foraminifera according to the descriptions of Swarczewsky 

 (1908) and Elpatiewsky (1909). A zygote (amebula) develops 

 into a typical adult Arcella agamont. This reproduces by agam- 

 ogony in no less than four ways if these observers are correct. 



A first method is by exogenous budding whereby agametes 

 (amebulae) are liberated to develop again into agamont s. Another 

 method is by multiple endogenous budding whereby many agametes 

 are formed each of which develops into an agamont. A third 

 method involves the desertion of the parent shell and of the primary 

 nuclei by the bulk of the protoplasm and secondary nuclei formed 

 by chromidia, and breaking up of this mass into agametes which 

 likewise develop into agamonts. Ultimately these agametes develop 

 into gamonts which become either macrogametocytes or microgame- 

 tocytes, or gamonts which conjugate as do the ciliates with an 

 interchange of chromidia (chromidiogamy) . The macrogametocytes 

 by multiple division give rise to macrogametes, and microgameto- 

 cytes to microgametes. A macrogamete is fertilized by a micro- 

 gamete, and the resulting zygote repeats the cycle. 



