124 PROTOPLASMIC AGE OF PROTOZOA 



the nucleus, the one superintending exclusively the processes having 

 to do with germinal life, heredity, and the race, the other having to do 

 only with the metabolic processes of the individual ? 



In connection with higher animals and plants we meet with con- 

 flicting answers to such a question. Weismann, Roux, and their 

 followers maintain — and their contention is strengthened by the con- 

 stantly increasing evidence as to individuality of the chromosomes 

 and their connection with specific characteristics of the adult organism — 

 that a specific inheritable substance — idioplasm — is always present in 

 the cell from the start, and is gradually sifted out with growth as the 

 various organs are formed. Others, notably O. Hertwig, take the view 

 that nuclear materials are fundamentally the same, and that as growth 

 advances, environmental changes affect and alter the original homo- 

 geneous stuff. It is in connection with the latter point of view that 

 R. Hertwig approaches the problem of dualism in the protozoan 

 nucleus (1907). He believes that "functional degeneration" becomes 

 localized in certain substances of the cell nucleus, so that a dualism 

 is gradually brought about through such degenerative changes, and 

 indicated, morphologically, by the difterent chromatin elements 

 scattered throughout the cell. Chromidia, therefore, according to this 

 point of view, would be the same as idiochromidia save for a difference 

 in potential, the latter having the possibilities of continued existence, 

 the former not. 



Neglecting, for the present, the question of original dualism in 

 nuclear substances in protozoa, we must accept the fact that there are, 

 at times, specific germ substances within the cell and localized in the 

 chromatin of the cell. In the higher animals the analogous germ 

 plasm becomes segregated and separated from the somatic plasm in 

 the form of germ cells or germinal epithelia. Differentiated from 

 somatic plasm during ontogeny, this racial protoplasm becomes 

 functional only after the period of maturity is reached. Similarly 

 with protozoa, there is, at periods of maturity, a definite germ plasm 

 distinct and separate from the somatic plasm. In some cases, like 

 the germ cells of higher animals, this specific racial substance is 

 early differentiated from the vegetative, functional, or somatic plasm. 

 Such is the case in infusoria, where, in Paramecium aurelia, for 

 example, germ nuclei and functional vegetative nuclei are differ- 

 entiated as micronuclei and macronuclei, respectively, after the third 

 division following conjugation; and such is the case in arcella and 

 allied forms where the germ plasm is not aggregated in a compact 

 micronucleus, but as idiochromidia is scattered throughout the cell. 



In other cases the germinal and somatic parts are not separated 

 until later in the life history, or in some cases not until full maturity, 

 when for the first time chromatin of conjugation and of vegetative 

 function can be distinguished. Such is the case in Ameha froteus, in 



