HEREDITY AND VARIATIONS IN PROTOZOA 569 



in the nutrient medium and under conditions of sunlight or of 

 artificial light he was able to cause a change of the thirty-two-cell 

 colony Eudorina elegans into the flat, colonial sixteen-cell type of 

 Gotiium pectorale, and Gonium pectoraJe into Eudorina elegans. With 

 return to the normal medium all such changed organisms reverted 

 to their respective genotj-pes. 



Experiments of this ty^e and others to be described below show 

 that changes in organization can undoubtedly be produced in 

 Protozoa. If such changes are permanent they may be interpreted 

 as mutations; if not permanent they ha^'e little more value than 

 the fluctuating variations which accompany changes of metabolism. 

 The great majority of changes which have been described are cen- 

 tainly not mutations but illustrate the flexibility of protozoan 

 organizations and broaden the limits within which fluctuating varia- 

 tions are known to occur. Such variations ultimately revert to type 

 and although they may last for many generations by division, they 

 have no permanent effect upon the organization. Jollos (1913) 

 terms them "enduring modifications" (Dauermodificationen). 

 Other frequently-cited illustrations of this type of variations have 

 to do with the effects of minute doses of poison on the organi- 

 zation. Some races of Trypanosoma for example, may become 

 adapted and immune to weak doses of arsenic— the so-called 

 poison-fast, arsenic-fast, atoxyl-fast races first described by Ehrlich. 

 Bignami (1910) thus interprets malaria relapses as due to quinine- 

 fast organisms. Such modified types retain their immunity for 

 long periods and through many successive generations of trans- 

 plants but they apparently belong to this type of enduring modifica- 

 tions. Gonder (1912) has shown that poison-fast races of Trypano- 

 soma lewisi, lose their acquired immunity by passing through the 

 rat flea. Also races of Trypanosoma without parabasal bodies 

 (Blepharoplastlose) first obtained by Werbitzski (1910) by injecting 

 pyronin into the host's blood, would live for many generations of 

 transplants without this kinetic element, but the parabasal body 

 ultimately reappears. Here too in all probability, belong the 

 so-called mutations in Ceratium ndtur described by Kofoid (1908), 

 and those in Radiolaria described by Haecker (1909) the observa- 

 tions in both cases being somewhat casual and not followed up 

 experimentally so that the matter of permanency is in doubt. 



The extensi^'e experiments on Paramecium made by Jollos 

 (1913, 1923), ofi'er many illustrations of change in organization and 

 subsequent return to normal, sometimes after many vegetative 

 divisions, sometimes after endomixis, and again only after conjuga- 

 tion. The eftect of arsenic acid calcium compounds, and extreme 

 temperatures, were lasting through one or more periods of endomixis 

 and conjugation, but such effects were ultimately lost. X significant 

 fact however is the difl'erence in effect produced by treatment with 



