H 



THE INVERTEBRATA 



Occasionally the protoplasm contains structures (trichocysts of 

 ciliates and mastigophora, Fig. 9, so-called ''nematocysts" in certain 

 dinoflagellates, Fig. 40, pole capsules of neosporidia, Fig. 82), 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 



Fig. 7. Euglypha alveola ta, x 60. From Hegner and Taliaferro, after Calkins. 



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

 are formed by the stiflening 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 filopodia (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 



