author's abstract of this paper issued 

 by the bibliographic service, september 29 



THE EFFECTS OF ENVIRONMENTAL FACTORS UPON 



THE HERITABLE CHARACTERISTICS OF ARCELLA 



DENTATA AND A. POLYPORA^ 



ROBERT W. HEGNER 



Department of Protozoology and Medical Zoology, School of Hygiene and Public 

 Health, The Johns Hopkins University 



SEVEN FIGURES 



While carrying on a series of experiments for the purpose of 

 testing the efficacy of selection as a means of isolating heritably 

 diverse lines within a clone of Arcella dentata, and later while 

 studying the nucleocytoplasmic relations in this species and in 

 A. polypora, several experiments were performed with the pur- 

 pose of determining the effects of environmental factors upon 

 the heritable characteristics of these organisms. 



If it is possible to modify organisms by means of external fac- 

 tors in such a way that the diversities produced will persist after 

 the disturbing factors have been eliminated, we may account 

 for the numerous heritable diversities that have been described 

 among the lower organisms by the presence of such factors in. 

 their environment. 



UNDERFEEDING 



During the selection work on Arcella dentata (Hegner, '19) 

 the organisms were supplied with an abundance of organic 

 matter shaken from the leaves and stems of aquatic plants. 

 The pond water in which this food material was suspended was 

 then diluted with distilled water. At first the number of spines 

 was used for purposes of selection, but later the diameter of the 

 shell was also employed, since the organisms w^ere found to be 

 remarkably constant in size, and diameter of shell and spine 



1 The studies presented in this paper are incomplete, but they are published 

 at this time, since the writer will probably be unable to carry on further experi- 

 mental work with Arcella in the near future. 



427 



