622 SCIENCE PROGRESS 



from one-tenth to three-fourths of the entire chromidial net 

 is removed, the descendants of the part that remains invariably 

 attain the normal condition of the family. When a large 

 Arcella is bisected and both nuclei are present in one-half, 

 the other half, without nuclei, always dies within a few days 

 without any visible attempt on the part of the chromidia to 

 form new nuclei. This is true even when only the nuclei are 

 removed and all the cytoplasm is left in the shell. The evidence 

 justifies the conclusion that the chromidia play no role in vegeta- 

 tive reproduction, and at this time have no influence upon the 

 size of the organism nor upon the characteristics of the shell. 



All the evidence derived from these extensive and inten- 

 sive investigations of Arcella indicates a definite quantitative 

 relation between nucleus, or rather chromatin^ and cytoplasm. 

 This evidence was obtained by accurately measuring these 

 materials in the living organisms, and is therefore more depend- 

 able than similar measurements of fixed and stained tissues. 

 Present theories of the reactions between chromatin and cyto- 

 plasm, with their widespread influence on the biological and 

 medical science, are based on insufficient and often erroneous 

 data. This situation can be improved by the direction of 

 investigators to the study of fundamental cell problems with 

 living organisms. 



Conclusion. — The investigations described above all prove 

 that in five species of Protozoa (Stylonychia pustulata, Difflugia 

 corona, Centropyxis aculeata, Arcella dentata, and A. polypora) 

 heritably diverse branches may be isolated from the descen- 

 dants of a single specimen obtained by asexual reproduction. 

 These heritably diverse branches resemble the diverse strains 

 that in each case were shown to exist in nature. The latter 

 may probably have originated in nature in a similar manner. 

 The chromatin-cytoplasmic studies of Arcella dentata and of 

 A. polypora are of particular interest because they deal with 

 the internal changes that accompany the differences in external 

 heritable characteristics. The correlation of these external 

 heritable characteristics, with the quantity and distribution 

 of the chromatin within the cell, is a considerable step forward 

 in our knowledge of the method of evolution. These researches, 

 however, leave many interesting problems for future investi- 

 gations, but " to travel hopefully is a better thing than to 

 arrive, and the true success is to labour." 



LITERATURE CITED 



Ackert, J. E., On the Effects of Selection in Paramoecium, Genetics, 1,387-405, 



1916. 

 Elpatiewsky, W., Fortpflanzung von Arcella vulgaris, Arch. f. Protist., 



10, 441-66, 1907. 



