192 Universiti/ of CaUfnnrio Puhlications in Zoologij [Vol. 16 



guished as different substances only by their ultimate behavior during 

 gametogenesis, as may be done in the Ciliata, already mentioned 

 above. In the eases cited here it is impossible to distinguish between 

 the chromidia formed by the nucleus during the growth period of the 

 cell and that formed by the extrusion of chromatin in the degeneration 

 of the nucleus, whereby the amount of chromidia in the cytoplasm is 

 greatly increased. No disintegration and disappearance of any 

 material and the preservation of another material distinct from it 

 can be shown to take place, as is the case in Paramaecium, where the 

 macronucleus dwindles and fades away during the process of conju- 

 gation. The facts, then, as brought out in the investigations of 

 these observers do not substantiate their claims for the presence of 

 two different kinds of chromatin. The alternative explanation above 

 proposed seems to adhere to the evidence more closely. 



In Plasmodiophora brassicae (Prowazek, 1905&) the gametic nuclei 

 are formed from the nucleus and the extruded chromidia are absorbed 

 in the cytoplasm. The chromidia in this case formed the "vegeta- 

 tive" chromatin and the nucleus the "generative" chromatin, just 

 tlie reverse of the relation assigned to them by the proponents of the 

 Ijinuclear theory in PatcUina. 



Another example which is a combination of the two methods noted 

 above is that described by Bott (1907, pi. 3, figs. 2-10) in the common 

 Pelomyxa at the time of gamete formation. The chromidia cast out 

 by the nucleus form secondary nuclei which in their turn undergo a 

 process of so-called "reduction" by casting out part of their chro- 

 matin, after which the gamete nuclei are formed (Bott, 1907, pi. 3, 

 figs. 12-16). The chromidia in this case are said to contain both vege- 

 tative and generative chromatin (Minchin, 1912). 



It may be pointed out, however, that the so-called ' ' reduction, ' ' as 

 well as the easting out of "vegetative" chromatin, is also found in 

 the ordinary binary fission process of Trichomonas (Kofoid and 

 Swezy, 1915a., h) and prior to the encystment of some amoebae (Wil- 

 son, 1915) which have no known relation to gamete formation. In 

 these cases it can hardly be called a differentiation of vegetative and 

 generative chromatin. It is more probably a phase of metabolism 

 rather than of segregation of hypothetical idioplasm. 



The casting out of material from the nucleus prior to gameto- 

 genesis is not limited to the Protozoa. According to Kellieott (1913), 

 "the chromatin of the nucleus which is not included in the spireme, 

 often indeed the greater part of the whole amount of this material, is 



