PHYSIOLOGY 101 



crystals are probably leucine, while the bipyramidal crystals con- 

 sist of a magnesium salt of a substituted glycine. Other crystals 

 are said to be composed of urate, carbonate, oxalate, etc. 



Another catabolic product is the melanin grains which occur 

 in many haemosporidians and which appear to be composed of a 

 derivative of the haemoglobin of the infected erythrocyte. In cer- 

 tain Radiolaria, there occurs a brownish amorphous mass which 

 is considered as catabolic waste material and, in Foraminifera, 

 the cytoplasm is frequently loaded with masses of brown granules 

 which appear also to be catabolic waste and are extruded from 

 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 Heliozoa, Radiolaria, 

 certain parasitic ciliates, etc., the extracellular secretions are eas- 

 ily recognizable as loricae, shells, envelopes, stalks, collars, mu- 

 cous substance, pigments which give the body a characteristic 

 coloration (p. 37), 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 



The Protozoa move about by means of the pseudopodia, flagel- 

 la, or cilia, which may be combined with internal contractile or- 

 ganellae. 



Movement by pseudopodia. The amoeboid movements have 

 long been studied by numerous observers. The first attempt to 

 explain the movement was by Berthold (1886), who held that the 

 difference in the surface tension was the cause of amoeboid move- 

 ments, which view was supported by the observations and ex- 

 periments of Btitschli (1894) and Rhumbler (1898). According to 

 this view, when an amoeba forms a pseudopodium, there prob- 

 ably occurs a diminution of the surface tension of the cytoplasm 

 at that point, due to certain internal changes which are continu- 

 ously going on within the body and possibly to external causes, and 

 the internal pressure of the cytoplasm will then cause the stream- 

 ing of the cytoplasm. This results in the formation of a pseudo- 

 podium which becomes attached to the substratum and an in- 

 crease in tension of the plasma-membrane draws up the posterior 



