130 J. A. DAWSON 



division, but these gradually disappeared, leaving two appar- 

 ently normal animals. A second monster occurred 'sponta- 

 neously,' but in this specimen the double characters were limited 

 chiefly to the peristomes. The same author ('93) obtained by 

 merotomy a series of multiple monsters which arose from the 

 double monsters which are invariably produced by the failure of 

 a 'merozoite' to complete the process of fission. Johnson ('93) 

 described a double monster in Stentor where the duality was 

 limited to the anterior part of the body. All traces of duality 

 disappeared in a few days. Simpson ('01) observed a double 

 Paramecium which had arisen by the failure of an exconjugant 

 to complete fission. Here the two bodies formed one continu- 

 ous animal which gave off daughter cells from each end for three 

 generations, after which it developed further abnormalities of 

 form and later died. Prowazek ('04) obtained double monsters 

 from fragments of Stentor. The same author ('04 a) observed 

 in degenerating cultures of Stylonychia a certain amount of 

 hyperregeneration. He figured an individual which had two 

 posterior ends while the mouth and cirri had suffered marked 

 reduction. Jennings ('08) described various abnormalities 

 occurring in.cultures of Paramecium. In particular he obtained 

 a race with a marked tendency to form chains, due to the failure 

 of individuals to complete the process of fission. Occasionally a 

 double individual pulled apart, producing paramecia with pos- 

 terior spines which were handed on to the posterior daughter 

 celts for a few generations. Mast ('09) described double and 

 triple monsters in Didinium which apparently consisted of indi- 

 viduals fused posteriorly. No explanation was given of the 

 origin of these monsters, although the author pointed out that 

 they obviously had not arisen from a failure to complete fission, 

 since the posterior ends were always in contact. In only one 

 case was an attempt at reproduction noted. Calkins ('11) pro- 

 duced double and multiple monsters by cutting paramecia. 

 Vitality was weak in these abnormal forms and death usually 

 occurred in a short time. Peebles ('12) obtained, by cutting, 

 fragments of paramecia which did not complete fission and thus 

 formed 'chain monsters.' Stocking ('15), working on the in- 



