26 



GENERAL ORGANIZATION OF THE PROTOZOA 



(c) Plastids. — In addition to the basic substances making up 

 the fluid protoplasm there are larger or smaller granules of different 

 kinds embedded in the alveolar or interalveolar material; these 

 granules may be food particles ready for assimilation, waste particles 

 waiting for excretion, metaplasmic particles like oil drops, pigment 

 grains, and the like, or foreign particles like sand grains, calcium, 

 silica, etc., to be used in building shells or stalks. 



The plastids that are formed in a great many protozoa, especially 

 in those types which lie on the boundary line between the lower plants 

 and the protozoa, may have a considerable economic importance. 

 Many of them are starchy in nature, i. e., formed products to be used 



Fig. 9 



A complex polythalamous shell (schematic) of Operculina. (After Carpenter.) The shell 

 is represented as cut in different planes to show the distribution of the canals (a', a", a'"); 

 c, c, c, the outer chambers with double walls (d, d, d), one of which is shown in section (g). The 

 chambers communicate by apertures at the inner ends of the septa (e), and by minute pores 

 (/). The outside (6) of the shell is marked by the radial septa. 



as food; others are starch-forming centres or pyrenoids, which are 

 usually embedded in plastids of large size, called chromatophores from 

 the color they possess. These colors, due to some form of chlorophyl, 

 may be bright green like the foliage of higher plants, or red, orange, 

 yellow, brown, or black, according to the nature of the materials which 

 combine with the chlorophyl. When great numbers of these color- 

 bearing protozoa are massed together the result is a brilliantly colored 

 area; red snow, for example, being due to aggregates of hematococ- 

 cus, the red coming from the color of the minute chromatophore in 

 each small cell. Similarly, great patches on the sea may be colored 

 orange by the presence of noctiluca, or red by peridinium, while 



