PROTOZOA II 



dilates and mastigophora, Fig. 9, so-called ''nemato cysts " in certain 

 dinoflagellates, Fig. 40, pole capsules of neosporidia, Fig. 81), from 

 which threads can be shot out upon the surface of the body. The 

 function of these threads is often doubtful, but it has been shown that 

 the trichocysts of Paramecium are fixing organs, others which lie 

 around the mouth of their possessor (Cyathomonas, Fig. 39 C; etc.) 

 seize prey, and the pole capsules serve to anchor spores to the lining 

 of the host's gut. The threads of " nematocysts " and pole capsules 

 are coiled up in vesicles before they are shot out; those of tri- 

 chocysts are formed by the stiffening of an extruded secretion. 



The motile organs of the Protozoa are of several kinds, each of which 

 is mainly found in one of the classes of the phylum. Pseudopodia are 

 temporary protrusions of protoplasm. They are of various types — ■ 

 blunt lobopodia (Figs. 54, 59), fine jilopodia (Fig. 7), branching and 

 anastomosing rhizopodia (Figs. 61 , 65), and axopodia (Fig. 71) with an 

 internal supporting filament. They are used in various ways and for 

 various purposes. Their mode of formation is not fully understood, 

 but it is clear that, at least in many cases, they do not arise, as has been 

 alleged, by alterations in the surface tension of the protoplasm, and 

 it is probable that the movement {amoeboid movement) in the course 

 of which they are formed is not fundamentally different from the 

 movements of muscles, or cilia, or flagella. Granules may often be 

 seen to stream up and down the axopodia and rhizopodia. Flagella 

 are lashes, long and usually few in number, which by a rowing 

 (Fig. 10) or by an undulating motion (Fig. 11) draw or propel the 

 body or attract particles to it. In the rowing stroke the flagellum is 

 held rigid and slightly concave in the direction of the stroke; in 

 recovering its position it bends as it is drawn back, so that less 

 resistance is offered to the medium. When, as is usually the case, the 

 flagellum beats obliquely, or the undulations pass around as well as 

 along it, the body rotates as it advances, or if it be fixed a whirlpool 

 is set up. Down each flagellum runs an internal thread, the axial 

 filament, which, on entering the body or at some distance within it, 

 joins a basal gramde.^ The latter is in most cases connected to the 

 nucleus by a thread or threads known as rhizoplasts (Fig. 47 A). 

 Sometimes it lies against the nucleus. Rhizoplasts may connect it 

 to other structures, notably in many parasitic flagellates to a body of 

 unknown function called the. parabasal body . The " kinetonucleus " 

 of Trypanosoma (Fig. 47 B) is a body of this class, which possibly in- 

 cludes structures of more than one kind. Sometimes, as in Trypano- 

 soma, a flagellum runs for some distance parallel with the surface of 

 the body and is connected to it by a film of protoplasm known as an 



^ This structure is also called the blepharoplast, but as that name has also 

 been applied to parabasal bodies its use is best avoided. 



