THE AMEBIC AX X ATU RALIST 



[Vol.XLV 



variability; while the organism as a whole was strongly 

 resistant to all kinds of environic influences, and actual 

 alterations were extremely rare. Most of the supposedly 

 acquired characters disappeared in two or three gener- 

 ations by fission, although one was followed for twenty- 

 two generations. The new character was borne by only 

 one of the pair produced by a division, except in rare 

 instances, and in only one case was there found such 

 modification as to produce a race bearing the odd char- 

 acter in which the feature in question was imperfectly 

 transmitted in series of asexual generations.' 1 



The results of Woltereck with Daphnia offer some- 

 thing by way of contrast and also serve to illustrate the 

 necessity for continuation of parallel cultures for the 

 purpose of comparison of divergent forms and the nor- 

 mal. The particular group of this crustacean furnish- 

 ing the experimental material is taken to be very var- 

 iable, and it was subjected to over-feeding with the im- 

 mediate result that the variability of the form of the head 

 appeared to be widened, the size of this structure being 

 increased. This disappeared when lots from the culture 

 •were restored to normal conditions in the earlier stage of 

 the work. After three or four months of over-feeding, 

 the form of the head came within narrower limits, and 

 fewer aberrants were seen, while lots returned to normal 

 conditions, showed a slower restoration of the original 

 form of the head. Two years after the cultures were 

 begun, it was found that the original head form was not 

 displayed by young restored to normal nutrition condi- 

 tions, the larger helmet being persistent. It seems 

 fairly certain that a new genotype resulted from the long- 

 continued action of the culture medium. 10 



