SPECTRAL COLOR AND STIMULATION 491 



days Pandorina became very abundant while the other organ- 

 isms practically disappeared. A few days later Eudorina de- 

 veloped, while Pandorina gradually disappeared. Thus by 

 watching these pools many of the species studied were secured n 

 any desired numbers and practically pure. Among these were 

 several of which ordinarily only a few scattered individuals are 

 found, e.g., Euglena tripteris, Trachelomonas, Eudorina, and 

 Gonium. This fortunate location of an abundance of excellent 

 material close at hand greatly facilitated the work undertaken. 

 In fact it would otherwise have been quite impossible to have 

 so thoroughly covered such a large field in the few months at 

 my disposal. The following fifteen species were fairly thoroughly 

 investigated with reference to responses to colors, and a number 

 of others were superficially studied. Trachelomonas, Chlamy- 

 domonas, and Phacus each one species; Euglena five species, 

 Gonium, Pandorina, Eudorina, Spondylomorum, Lumbricus, 

 Arenico^a (larvae) and blowfly (larvae) each one species. Details 

 concerning these studies and the results obtained are presented 

 in the following pages. 



EXPERIMENTAL OBSERVATIONS 



Introduction 



Success or failure in attempting to ascertain the relation be- 

 tween wave-length and stimulation with the method previously 

 described depends largely upon the condition of the organisms 

 used. The more precisely they orient, the more strongly posi- 

 tive or negative and the more active they are, the more accurate 

 the results will be. It is consequently essential, especially for 

 those who may wish to repeat these experiments, to know as much 

 as possible about the treatment the organisms received preced- 

 ing the tests, their habits and habitats and the conditions under 

 which they are likely to respond in a way most favorable to the 

 work. I shall therefore in this section pi'esent, in addition to 

 the results obtained, some of the characteristics of the responses 

 of the organisms, their habits, and their environment which are 

 intimately related to the observations made. 



