192 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII. 



not only is this the case but it seems very questionable whether 

 the changes originated by use and disuse are in any way more 

 hereditary than they are in Metazoa. There are no direct ob- 

 servations to test whether any of the cilia in an Infusorian 

 could be strengthened ^y increased use, either in connexion 

 with some new kind of food, or with a struggle against stronger 

 currents in water ; but we need not doubt that in these or- 

 ganisms, small and relatively simple as they are, functional hy- 

 pertroph}'^ and atrophy play the same role as in larger and more 

 complex beings. I would refer my readers to Wilhelm Roux's 

 excellent treatise on this subject in the higher organisms. If 

 certain cilia in an Infusorian were to increase in size as the result 

 of more active function, how can we conceive the transmission 

 of this change to the hereditary substance contained in the 

 nucleus ? The path is certainly shorter than that from the 

 human brain and finger muscles to the reproductive cells ; but 

 distance, hke all measurements, is only a relative idea, and the 

 question arises whether there is any ground for the assumption 

 that such increased growth in the cilia causes any corresponding 

 change in the nuclear substance of the animal. But if this does 

 not occur, any inheritance of acquired characters is as impos- 

 sible as it is in man. How, for instance, can an increase of the 

 adoral ciliated zone of a Stenfor be transmitted to both the 

 products of its fission, considering that the hindmost of these 

 has to form an entirely new mouth ? It might perhaps be 

 pointed out that R. Hertwig believes he has seen the mouth 

 of the hinder offspring arise by budding from that of the an- 

 terior ; but the artificial division of Sfentor, as effected by 

 Gruber, proves that the mouth of the posterior part is not 

 dependent on the existence of the original mouth, but can 

 arise quite independently, provided only that a portion of the 

 nucleus is present. 



I therefore hold that a belief in the inheritance of acquired 

 characters by the highly differentiated Protozoa, as well as by Me- 

 tazoa, must be opposed, and I imagine that the phyletic modifications 

 of Protozoa arise from the germ-plasm, that is from the idioplasm 

 of the nucleus. 



We can now understand why nature has laid so much stress 

 on the periodical mingling of the nuclear substances of two 

 individuals, — why she has introduced amphimixis among these 



