780 MORPHOGENESIS 



already in progress. Young excysted specimens have a lowered regenera- 

 tive capacity because physiological restoration is incomplete; with in- 

 creasing age, the normal vegetative existence is resumed and the re- 

 generative capacity is restored to the normal level (Moore, 1924). 



Recently Garnjobst (1937) described an interesting case of what she 

 called regeneration cysts in Stylonethes. Anterior and posterior halves of 

 bisected organisms round up and secrete a cyst wall about themselves. 

 Regeneration occurs within the cysts. Excystment is spontaneous, re- 

 leasing minute but perfectly formed individuals. Garnjobst maintained 

 these excysted regenerates until they formed reproductive cysts, the nor- 

 mal condition for binary fission in the species. 



3. RACIAL DIFFERENCES 



The amount of literature on genetics and regeneration is pitifully 

 small. Perhaps this is due, in part, to the difficulty of making clear-cut 

 distinctions between the total inherent capacities and the strictly extrinsic 

 factors which are responsible for variations in the expression of these 

 capacities. 



In contrast with Balbiani's (1893) conclusion that Paramecium 

 caudatum does not regenerate as do other Protozoa, Calkins (1911b) 

 found that the power of regeneration varied in different giant races of 

 P. caudatum. Of these races for which data are given, one produced 

 regenerates in approximately one percent of the cases; another race 

 produced 10 percent; and a third produced 30 percent. Mention is made 

 of a fourth race, which showed 100 percent regeneration (data not 

 given). Peebles (1912) likewise reported four races of P. caudatum 

 which, according to her conclusions, showed wide variations in regenera- 

 tive power. Regeneration in the different races varied from 23 percent 

 to 67 percent for anterior cut-offs and froni 25 percent to 100 percent 

 for posterior sections (her Table 3, p. 164). In view of her generaliza- 

 tions that "Paramecium taken from a pure line will regenerate in ninety 

 cases out of a hundred if the cytoplasm is in a viscid state and the ani- 

 mals are well-fed" (p. 165) and that "The power to regenerate is not 

 so much a characteristic of the race as it is an indication of the vitality of 

 the individual cell" (p. l65), the data tabulated in percentages only do 

 not distinguish the racial from the individual differences. 



M. E. Reynolds (1932) described experiments with a non-regenerat- 



