54 BIOLOGY OF THE PROTOZOA 



being due, probal^Iy, 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 Blephorisma undulans, for example, may be colorless 

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

 in color. In many cases the pigment is accumulated in masses of 

 varying size representing excretory matters of one kind or other. 

 Thus we find the black pigment granules of Metopus sif/moides and 

 Tillina magna, or the brown pigmental masses (phseodium), char- 

 acteristic of the trip\'larian 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. 21). 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 IVIitrophanow has shown for Paramecium, 

 and as I have also observed (un])ublished) in the case of Actinohohis 

 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. The trichites are stiff, 

 usually rod-like supporting structures and are rarely discharged 

 (for discussion of the distribution and functions of these structures 

 see Chapter III). 



All of the structures described above, together with the defecatory 

 materials such as sand grains, shells and tests of other organisms 

 taken in as food, etc., which never form a part of the living sub- 

 stance, make up, together with nuclei and kinetic elements which 

 will be considered in the following Chapter, the granular aggre- 

 gate of colloidal substances which we see in living protozoon pro- 

 toplasm. Their chemical and physical reactions and interactions, 

 in abeyance during encystment, combine to furnish the manifold 

 physiological activities of the organism and to distinguish living 

 things from lifeless matter. Their possibility' of living activity 

 ends only with death of the organism, and death, one of the most 

 remarkable phenomena of life, is the disintegration of the proto- 

 plasmic organization which forms the physical basis of vitality. 

 Accepting the view that spontaneous generation of living things 

 under present conditions is highly improbable and for which there 

 is no acceptable evidence, it follows that the protoplasm of all things 

 living today has been continuously living since life appeared on the 

 earth. How it was originally formed and under what cdnditions, 

 are matters of speculation with which we are not concerned here. 



Protozoa, finall\-, should be regarded as single-celled organisms 

 notwithstanding the views of Whitman et al. concerning the inade- 

 quacy of the cell theo^^' as interpreted by Whitman, Gurwitsch, or 



