GENERAL MORPHOLOGY 27 



drinking waters are not infrequently made unsightly because of the 

 red coloring matters of Euglena sancjuinea, or of the yellow coloring 

 matters of dinobryon or uroglena. 



In some cases the pigment is due to collections of waste materials 

 stored up in the cell, products of proteid metabolism held in reserve 

 for some useful purpose, or to be voided to the outside. The black 

 pigment of metopus or of tillina is a waste product of this nature, 

 while the yellow to brown pigment of some of the colony forms is 

 utilized in building the stalk. 



The fats, oils, and other metaplasmic products, stored up in these 

 minute cells, minute as they are in the individual, are, collectively, a 

 great nuisance, or, in some parasitic forms, may be a menace to the 

 life of the host. Potable waters are frequently rendered unfit to drink 

 because of the odors and tastes due to these products of protozoan 

 vitality. Such odors are rarely due to putrefaction of the organisms, 

 but rather to the liberation of the minute drops of oil upon disintegra- 

 tion of the cell bodies. As crushing a geranium leaf causes minute 

 drops of oil to be thrown into the air, giving the fragrant perfume of 

 the plant, so disintegration of a uroglena colony, crushed by the 

 pressure in pumps and mains, liberates the minute oil drops stored 

 up in the inner protoplasm, but the cod-liver oil smell which they 

 give to the water is far from fragrant. Such water is harmless 

 so far as the health is concerned, but very offensive to the esthetic 

 sense. So characteristic are these metaplasmic products, that many 

 kinds of protozoa can be recognized in drinking waters simply by 

 the odors they impart. 



The oils, which in the majority of cases, like fat, are probably a 

 reserve store of nutriment, may, in some cases, become useful for 

 purposes of protection. An interesting case of a possible protecting 

 function is that of noctiluca, where the particles of oily matter are 

 rapidly oxidized upon exposure to the air, resulting in a brilliant flash 

 of light, and giving .one great source of the phosphorescence in the sea. 

 The possibility of a protective function comes from the fact that the 

 fatty material is thrown out of the body upon irritation, and the flash 

 of light may scare away small enemies. 



Other plastids that are used for purposes of protection are tricho- 

 cysts and trichites. These are minute structures derived from 

 the nucleus (Mitrophanow, 1904) and arranged radially about the 

 entire periphery, as in paramecium, frontonia, etc., or in certain 

 regions only, as in dileptus or chilodon. When the organism is 

 irritated the contents of the capsules are thrown out with considerable 

 force, and the poison which they contain is strong enough to paralyze 

 any single-celled opponent, or, possibly, as Mast ('09) suggests, they 

 form, after their discharge, a dense protective envelope which cannot 

 be penetrated by small enemies. Sometimes they are used as weapons 



