216 



THE PROTOZOA 



between swarm-spores, either amoebulse or flagellulse. The microg- 

 amy is isogamous or slightly anisogamous ; macrogamy, as in other 

 cases, is perfectly isogamous. Microgamy occurs, as has been seen 

 (p. 148), in Arcdla in addition to chromidiogamy ; and, according 

 to a recent note of Zuelzer (86, p. 191, footnote), syngamy between 

 free swarm-spores occurs in Difflugia also. 



As regards the life-cycle of the Sarcodina, there remains still so 

 much to be discovered that to generalize is both difficult and 

 dangerous. Even in the commonest forms, such as Ama&a proteus, 

 the complete life-cycle has not been yet worked out. In some 



FIG. 85. Changes in the form of an amoeba under the influence of differences 

 in the [surrounding medium. A G, In its natural medium (water) : A, 

 contracted ; B, beginning to throw out pseudopodia ; 0, Umax-form. D F, 

 Forms assumed after addition of potash-solution : I), contracted, beginning 

 to throw out pseudopodia ; E, F, radiosa-fov&a. After Verworn. 



cases the life-cycle appears to be of comparative^ simple type, and 

 the species is monomorphic or nearly so, as in Actinosphcerium ; 

 in other cases there is a well-marked alternation of generations, 

 with dimorphism in the adult condition, as in Trichosphcerium 

 (p. 182), the Foraminifera, etc. 



Classification. The Sarcodina are subdivided into a number of 

 orders, the distinctions between which are based principally on the 

 characters of the pseudopodia and of the skeleton, when present ; 

 in more highly differentiated forms, such as Radiolaria, the internal 

 structure of the body is also taken into account. In the primitive 



