134 BIOLOGY OF THE PROTOZOA 



more widely distributed through the entire group of Protozoa, 

 forming the substratum upon which, or between layers of which, 

 shell materials are deposited, while cups, tests or "houses," cyst 

 membranes, stalks, etc., are formed directly from its substance. 

 Shell and skeleton materials such as calcium carbonate, silica, 

 strontium sulphate, etc., are likewise formed as results of metabolic 

 activity, sometimes continuously, as in the lime-stone shells of the 

 Foraminifera, and sometimes periodically at intervals of saturation 

 (dictyotic or lorication moment) as in the formation of the charac- 

 teristic silicious skeletons of the Radiolaria. 



Pigments of various hues are also frequently found in Protozoa. 

 In some cases, as in Actinosphaerium eichhornU, they are formed as 

 a final product of degeneration of chromatin granules (chromidia) ; 

 in other cases they are products of metabolic activities following 

 the digestion of specific kinds of food, as melanin pigment, brown or 

 black in color, which follows the digestion of hemoglobin by malaria- 

 causing hemosporidia (Plasmodium species). Specific coloring 

 matters are found here and there, especially amongst the ciliates, 

 which have nothing to do with chlorophyll and which are named 

 according to the organism in which they are found. Thus the blue 

 coloring matter sometimes called stentorin, is characteristic of 

 Stentor coeruleus and some species of Folliculina; a red pigment of 

 Mesodinium rubrum; violet of Blepharisma undulans, etc. ; the colors 

 being due, probably, to the kind of food that is eaten, since the 

 pigmentation of the same species is not constant, some forms in the 

 same culture of Blepharisma undulans, for example, may be colorless 

 while others are more or less bright pink, or violet, or even purple 

 in color. The suggestion has been made that specific products of 

 hydrolysis of certain kinds of food act as intravitam stains on the 

 protoplasm, thus producing the characteristic colors. In many 

 cases the pigment is accumulated in masses of varying size repre- 

 senting excretory matters of one kind or other. Thus we find the 

 black pigment granules of Metopus sigmoid es and of Tillina magna, 

 or the brown pigmental masses (phaeodium), characteristic of the 

 tripylarian Radiolaria. 



Other metaplastids that are useful for purposes of protection or 

 support, are the peculiar trichocysts and trichites found in the 

 ciliates and about which there is very little definite information 

 (Fig. 35, p. 67). They are usually embedded in the cortex when fully 

 formed but the trichocysts at least appear to be formed in the 

 vicinity of the nucleus as Mitrophanow has shown for Paramecium, 

 and as I have also observed in the case of Artinoboliiia radians. The 

 trichocysts at rest are capsules filled with a densely staining (with 

 iron hematoxylin) substance which is thrown out in the form of 

 long threads when the organisms are violently irritated as with 

 poisons of one kind or another. They appear to be connected with 



