122 PROTOZOOLOGY 



inifera, the cytoplasm is frequently loaded with masses of brown 

 granules which appear also to be catabolic waste and are extruded 

 from the body periodically. 



While intracellular secretions are usually difficult to recognize, 

 because the majority remain in fluid form except those which pro- 

 duce endoskeletal structures occurring in Foraminifera, Heliozoa, 

 Radiolaria, certain parasitic ciliates, etc., the extracellular secretions 

 are easily recognizable as loricae, shells, envelopes, stalks, collars, 

 mucous substance, etc. Furthermore, many Protozoa secrete, as was 

 stated before, certain substances through the pseudopodia, tentacles 

 or trichocysts which possess paralyzing effect upon the preys. 



Movements 



Protozoa move about by means of the pseudopodia, flagella, or 

 cilia, which may be combined with internal contractile organellae. 



Movement by pseudopodia. Amoeboid movements have long been 

 studied by numerous observers. The first attempt to explain the 

 movement was made by Berthold (1886), who held that the differ- 

 ence in the surface tension was the cause of amoeboid movements, 

 which view was supported by the observations and experiments of 

 Butschli (1894) and Rhumbler (1898). According to this view, when 

 an amoeba forms a pseudopodium, there probably occurs a diminu- 

 tion of the surface tension of the cytoplasm at that point, due to 

 certain internal changes which are continuously going on within the 

 body and possibly due to external causes, and the internal pressure of 

 the cytoplasm will then cause the streaming of the cytoplasm. This 

 results in the formation of a pseudopodium which becomes attached 

 to the substratum and an increase in tension of the plasma-mem- 

 brane draws up the posterior end of the amoeba, thus bringing about 

 the movement of the whole body. 



Jennings (1904) found that the movement of Amoeba verrucosa 

 (Fig. 44, a) could not be explained by the surface tension theory, 

 since he observed "in an advancing amoeba substance flows for- 

 ward on the upper surface, rolls over at the anterior edge, coming 

 in contact with the substratum, then remains quiet until the body 

 of the amoeba has passed over it. It then moves upward at the 

 posterior end, and forward again on the upper surface, continuing 

 in rotation as long as the amoeba continues to progress." Thus 

 Amoeba verrucosa may be compared with an elastic sac filled with 

 fluid. Dellinger (1906) studied the movement of Amoeba proteus, A. 

 verrucosa and Difflugia spiralis. Studying in side view, he found 

 that the amoeba (Fig. 45) extends a pseudopod, "swings it about, 



