240 BIOLOGY OF THE PROTOZOA 



(Janicki) and others. In these cases, as in Trypanosoiim leivisi, 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 (microsphferic shell, 

 Fig. 119, B). When fully grown the chromidia-laden protoplasm 

 breaks up by multiple division into a great number of amoeboid 

 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 (macrosph?eric shell Fig. 1,19, 

 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 microsphteric 

 individuals (Fig. 119, A). Similarly in ArceUa 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 (amoebula) develops 

 into a typical adult ArceUa agamont. This reproduces by aga- 

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



A first method is by exogenous budding whereby agametes 

 (amoebula?) are liberated to develop again into agamonts. 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. 



Multiple di^'ision is safely established for a number of Radiolaria 

 although it is not yet determined whether the products are agametes 

 or gametes. In many cases the flagellated swarmers which are 

 thus formed by one individual are large while those formed from 

 another indi"\'idual are smaller. This has led to the view that the 

 swarmers are anisogametes, but actual fertilization has not been 

 safely established. They are formed from the materials of the cen- 

 tral capsular protoplasm, which at first uninucleate, becomes multi- 

 nucleate by repeated divisions of the nucleus. Comparatively 



