LIFE HISTORY OF TWO RARE CILIATES 381 



might have been avoided or at least averted, had the proper 

 conditions, essential to the well-being of the organism at this 

 crisis, been found. 



B. Nucleus -plasma -relation 



There has been a growing tendency in recent years to regard 

 the protozoan nucleus as composed of two distinct substances, 

 similar in structure but differing in function; one a trophonu- 

 clear matter controlling the vegetative furfctions of the cell; 

 the other a substance concerned primarily with the reproduc- 

 tive activities of the organism. 



The conception of the double nature of the nucleus is due 

 to R. Hertwig, who in 1887 discovered a mass of extranuclear 

 substance in Arcella, forming a band between the two vegeta- 

 tive nuclei. In 1889 he observed the formation of secondary 

 nuclei from this extra-nuclear band to which in 1902 he applied 

 the name 'Chromidial-netz.' 



We are indebted to Schaudinn ('03) however, for the true 

 interpretation of this chromatin mass. He found that from 

 this extra-nuclear substance, in the case of Polystomella, Cen- 

 tropyxis and Chlamydiophrys minute nuclei are formed which 

 become the nuclei of conjugating gametes. He concluded, there- 

 fore, that in these forms the chromidial-netz is sexual chromatin 

 existing in combination with the trophic chromatin during the 

 vegetative condition. 



The work of Hertwig and Schaudinn has been greatly ex- 

 tended by Brandt ('02 and '05), Prowazek ('04), Goldschmidt 

 ('05), Lister ('06), Doflein ('07), Calkins ('07), and others. Gold- 

 schmidt concluded, as a result of his work on nematodes and 

 protozoa, that every animal cell is binucleate, possessing both 

 trophic and sexual chromatin. These substances are usually 

 combined in one body, the amphinucleus, but the separation 

 of the two elements may be more or less complete. 



We may distinguish three distinct degrees of nuclear differ- 

 entiation among the protozoa; first, a nucleus in which both 

 functions, vegetative and reproductive are combined, the so- 

 journal OP MORPHOLOQT, VOL. 23, NO. 3 



