MORPHOGENESIS 775 



hibits growth but does not impair the ability to regenerate; the latter 

 remains the same as for normally fed specimens. Extreme starvation 

 leads to a state of depression in which fragments attempt but never 

 achieve full structural restitution. The cases of physiological reorganiza- 

 tion, as reported by Lund (1917) and Hetherington (1932) for Bur- 

 saria and by Dembowska (1938) for Stylonychia, confirm the validity 

 of Sokoloff's conclusion. 



Chejfec (1932), following Balbiani (1893), Calkins (1911b), and 

 Peebles (1912), accepted the possibility of a low potential for regenera- 

 tion in Paramecium caudatum. He attempted to increase the regenerative 

 power in this species by altering the environment in several ways. The 

 experimental organisms, placed under conditions of starvation or in 

 acidified media (initial pH 4.5-6.0), regenerated more readily than the 

 control group grown in ordinary hay infusion. 



A variety of alkaloids such as morphine, strychnine sulphate, and so 

 forth, when administered in sublethal concentrations to Blepharisma 

 undulans, cause the pink-colored pellicle to be discarded (Nadler, 1929) . 

 Animals so treated readily regenerate new pellicles if returned to the 

 customary medium. If they are left in the alkaloid-containing medium, 

 the pellicle does not reappear. Naked but otherwise normal organisms 

 were maintained in this fashion for 110 days by Nadler. 



Since reparative processes are set in motion by unfavorable alterations 

 of an organism or the medium in which it lives, almost the entire sub- 

 ject of regeneration could be exhaustively but not effectively treated 

 under this heading. The many other pertinent publications are discussed 

 throughout the chapter. 



2, CYCLICAL VARL\TIONS 



Division cycle. — The experiments of Calkins (1911a) on Ur onychia 

 transfuga were designed to test whether or not Protozoa are capable of 

 regenerating with equal facility during the various phases of cell division. 

 It appears that prior to that time regeneration was generally assumed to 

 be independent of cyclical phenomena. Operations performed on Uro- 

 nychia shortly after cell division showed the regenerative capacity of the 

 individual to be feebly developed. The presence of both macronucleus 

 and micronucleus was essential for such cases of regeneration as did 

 occur at this period. At the mid-interphase, eight to sixteen hours after 



