370 PRESENT PROBLE^IS IN EVOLUTION AND HEREDITY. 



stroiig:ly against this as a universal principle, for many maternal and 

 paternal structures are preserved in their absolnte integrity for gener- 

 ations without the least indication of mixture. 



Cell forces and heredity. — We have thus far been considering only 

 the chromatin as the heredity substance p((r excellence, and have dis- 

 regarded for tlie time the archo-plasm or dynamic material of the cell. 



If we advance upon the hypothesis that a typical cell contains the 

 more or less passive chromatin, and the archoplasm playing- upon this 

 chromatin in conrse of every phase of re-distril)ution, it seems a priori 

 improbable that elements which are associated with every vital change 

 should be dissociated in the phenomena of heredity. We might supi30se 

 that the mechanics of karyokinesis are exactly similar in every cell 

 of one individual, but it is highly improbable that they should be ex- 

 actly similar in two individuals. We should therefore anticipate the 

 joint transmission of the chromatin and archoplasm, implying by the 

 latter the dynamic centers especially connected with hereditary function 

 as distinguished from the general functions of metabolism. 



This leads us to look for evidence from the lite of the cell in its 

 totality. We owe to Dr. Max Verworn* a fresh treatment of this 

 subject, based upon experimental researches among the Infusoria, 

 mainly by the extiri^ation method. As his experiments included only 

 the phenomena of living- cells in which the chromatin substance was 

 of course undifterentiated to the eye, he treats of the nucleus as a 

 wliole without distinction as to chromatin and achromatin. lie con- 

 cludes that the physiological importance of the nucleus is exhibited 

 in its constant interchange of materials with tlie remainder of the cell 

 body; only through this interchange does it influence the cell and 

 control its life processes. The interchange is in triple currents, «, 

 from outside of cell to cyto-plasm; b, from cyto-i)lasm to nucleus; c, 

 from nucleus to cyto-plasm. These movements of interchange are the 

 expression of life phenomena. He compares the role of the nucleus to 

 that of a cell organoid, like chlorojjhyll, as not constantly present but 

 as invaribly necessary to activity. Thus he believes even the most 

 lowly organized cells have nuclear centers, and that even bacteria are 

 differentiated into nuclear and extra-nuclear areas. Coupled with this 

 idea of nuchvar control is the somewhat paradoxical statement that 

 the nucleus is not a dynamic center, either automatic or regulating, 

 and the conclusion that the nucleus alone cannot be the seat of fer- 

 tilization and heredity, but both the nucleus and extra- nuclear pro- 

 toplasm must c( >nstitute the material basis of heredity. This conclusion 

 is in the direction of the general reaction of opinion which is now 

 taking place against the centralization of cell-government in the nucleus. 



Vague as they nnist necessarily be, our ideas of cell forces are some- 

 what further detined by the brilliant experiments of the llertwig 



" "Die Physiologische Bedeutung des Zellkerns/' ArcUv filr Physiology, 1891, pp. 

 113-115. 



