REPRODUCTION 213 



An enormous number of regeneration experiments have been con- 

 ducted on more than 50 ciliates by numerous investigators. Here 

 also the general conclusion is that the nucleus is necessary for re- 

 generation. In many cases, the macronucleus seems to be the only 

 essential nucleus for regeneration, as judged by the continued divi- 

 sion on record of several amicronucleate ciliates and by experiments 

 such as Schwartz's in which there was no regeneration in Stentor 

 coeruleus from which the whole macronucleus had been removed. 



A remarkably small part of a protozoan is known to be able to re- 

 generate completely if nuclear material is included. For example, 

 Sokoloff found 1/53-1/69 of Spirostomum ambiguum and 1/70-1/75 

 of Dileptus anser regenerated and Phelps showed portions down to 

 1/80 of an amoeba were able to regenerate. In Stentor coeruleus, 

 pieces as small as 1/27 (Lilly) or 1/64 (Morgan) of the original speci- 

 mens or about 70/jl in diameter (Weisz) regenerate. Burnside cut 27 

 specimens of this ciliate belonging to a single clone, into two or more 

 parts in such a way that some of the pieces contained a large portion 

 of the nucleus while others a small portion. These fragments re- 

 generated and multiplied, giving rise to 268 individuals. No dimen- 

 sional differences resulted from the different amounts of nuclear 

 material present in the cut specimens. Apparently regulatory pro- 

 cesses took place and in all cases normal size was restored, re- 

 gardless of the amount of the nuclear material in ancestral pieces. 

 Thus biotypes of diverse sizes are not produced by causing inequali- 

 ties in the proportions of nuclear material in different individuals. 



In addition to these restorative regenerations, there are physio- 

 logical regenerations in which as in the case of asexual and sexual re- 

 production, various organellae such as cilia, flagella, cytostome, 

 contractile vacuoles, etc., are completely regenerated. Information is 

 now available on the process of morphogenesis in regeneration and 

 reorganization in certain ciliates (Chatton and Lwoff, 1935; Bala- 

 muth, 1940; Summers, 1941; Faure-Fremiet, 1948; Weisz, 1948, 

 1951). 



References 



Balamuth, W. : (1940) Regeneration in Protozoa: a problem of 

 morphogenesis. Quart. Rev. Biol., 15:290. 



(1951) Biological studies on Entamoeba histolytica. III. J. 



Infect. Dis., 88:230. 



Barker, H. A. and Taylor, C. V.: (1931) A study of the conditions 

 of encystment of Colpoda cucullus. Physiol. Zool., 4:620. 



— (1933) Studies on the excystment of Colpoda cucul- 

 lus. Ibid., 6:127. 



