328 The Unity of the Organism 



and cytoplasm of the animal's body to their final position 

 in the ectoplasm. An essential constituent of the germ, as it 

 may be properly called, of each trichocyst, is a body which 

 from its familiar characteristics as to density, light refrac- 

 tion and stainableness, Tonniges does not hesitate to regard 

 as chromatin. It seems undoubted, consequently, that chro- 

 matin of the macronucleus contributes directly to the origin 

 of the trichocysts in Frontonia and probably in all related 

 protozoans. Figure 15 shows the germinal bodies, trch, in 

 the macronucleus, macr. and various stages and positions of 

 the trichocysts as they develop and make their way through 

 the cytoplasm. The details of development are highly in- 

 teresting and will be examined more closely in a later sec- 

 tion. The very brief account given here suffices to show 

 chromatin acting directly as "hereditary substance" in the 

 production of trichocysts. But, as we shall see later, while 

 chromatin is here an undoubted physical basis of heredity, 

 it is not the only substance that plays such a part in this 

 particular case. Nor should the reader neglect to notice 

 that the chromatin functioning thus belongs to the macronu- 

 cleus which, according to current interpretation, is not con- 

 cerned with reproduction but with nutrition, its chromatin 

 being called "vegetative." 



Perhaps the clearest cases among the protozoa of direct 

 contribution of the nucleus to the production of organs are 

 furnished by the origin of the flagella in some groups. A 

 good example is furnished by the soil amoeba Naegleria gru- 

 beri upon which Professor Kofoid has recently published a 

 short paper (figure 16a, 16b, 16c, 16d). Individuals of this 

 species change "on slight provocation under conditions of 

 laboratory culture," from an amoeboid, non-flagellate phase 

 (figure 16a) to a non-amoeboid flagellate phase (figure 

 16d). The nucleus of the animal is in the form of a single 

 karyosome situated within a heavy nuclear membrane. (Fig- 

 ure 16a). Professor Kofoid's description of the develop- 



