346 BIOLOGY OF THE PROTOZOA 



offspring were similarly distortions, while some, as with the Uroleptus 

 mobilis double individual, reverted to the single type. The double 

 individuals were maintained in culture for a period of five months 

 (sic) when they were abandoned, Chatton believing that they might 

 be continued indefinitely by division. Analogous double individuals 

 were obtained by Dawson (1920) by the fusion back to back of 

 amicro nucleate individuals of Oxytricha hymenostoma. The double 

 individuals reproduced double individuals for 102 generations by 

 division. Dawson's monsters ultimately died. The permanence 

 of Chatton's Glaucoma scintilla ns may well be questioned and it is 

 unfortunate that he discarded the race after only five months of 

 culture. The double Uroleptus at the age of five months was more 

 vigorous than at the outset, but like all other series of Uroleptus it 

 ultimately died. It lived and reproduced, however, for more than 

 fourteen months (see p. 244). 



Similarly with mutilations. The mutilated portions are passively 

 handed down to progeny by division, but the organization is not 

 affected and in the course of a few divisions the normal type is 

 regenerated. This was demonstrated by Jennings (190S) and con- 

 firmed by Calkins and by Peebles (1911, 1912) in cutting off the 

 anterior or posterior end of Paramecium, leaving a truncated indi- 

 vidual which did not regenerate but divided to form a perfect 

 individual from the posterior end and a truncated individual from 

 the anterior end (Fig. 108, p. 216); after a few divisions both ante- 

 rior and posterior individuals were perfectly normal. Abnormal 

 projections such as spines or clefts in the cortex, etc., are likewise 

 passively transmitted to descendants by division for a limited time, 

 but no permanent change in organization is brought about. 



In general the upshot of all experiments with poisons, heat, ab- 

 normalities, etc., is failure to modify the organization of Protozoa 

 in any permanent manner. The experiments of Jollos of treating 

 Paramecium at the time of reorganization are, however, possible 

 exceptions. 



Modifications of the organization which arise from within the 

 organism itself, on the other hand, may be permanent. Such 

 modifications are possible through the sifting out of germinal 

 characteristics in the course of continued metabolic activity and 

 division. Some are manifested by morphological characters which 

 afford a basis for selection on the part of the investigator. Experi- 

 ments to this end have been carried out mainly by Jennings and his 

 associates. The underlying principle in such selection work is that 

 a single individual from a "wild" population is the result of a great 

 number of hereditary characteristics stored up in the past through 

 amphimixis and united now in the organization of the single indi- 

 vidual. Such an individual, if cultivated under uniform conditions, 

 gives rise to progency showing diversities in structure or function 



