196 University of California Publications. Izoologt. 



while the lower portion, where the larvae were, was in darkness. 

 The aim here was, of course, to see if the animals could be 

 attracted upward. Although in some of these experiments the 

 lighted zone was brought down to within a few centimeters of the 

 larvae, the results were all negative. As the light rays in some 

 of these experiments were directed horizontally and not verti- 

 cally, the natural conditions were not exactly reproduced in these 

 particular instances. tStill another method of experimentation 

 consisted in placing a glass aquarium containing many specimens 

 indeterminately distributed in their swimming near the bottom, 

 in direct sunlight, to see if they would manifest a tendency to 

 assemble on either the light or the dark sides. Many trials 

 of this kind were made, always, with two exceptions, negative in 

 results. These exceptions were as follows: At the beginning 

 of an experiment on July 8, of a total of thirty-seven specimens 

 under observation sixteen were on the sunny side of the dividing 

 line, and twenty-one on the dark side. At the end of one hour 

 twenty-six were on the sunny side and ten on the dark. The 

 aquarium was now turned 180°, and at the end of another fifty- 

 five minutes twenty-four were on the sunny side and eleven on 

 the dark side. The conditions of experimentation enumerated 

 above as being essential to reliable results were certainly not 

 more favorable in these particular two that pioduced evidence of 

 positive phototaxis than in numerous others that produced no such 

 evidence. Whatever vitiating effect the departure from ideal 

 conditions of experimentation indicated in </ and c might have, 

 this, it would seem, should apply as well in those cases in which 

 positive results were indicated as to those in which negative 

 results were obtained. 



We conclude, therefore, that while our results are not entirely 

 beyond question, they strongly indicate that this tornaria reacts 

 very slightly if at all, either positively or negatively, to light of 

 the intensity to which it is subject in nature. 



We come then to our conclusion as to the immediate influence 

 that induces the upward swimming of this tornaria; that causes 

 it to remain in suspension during its larval life proper; and that 

 then determines the manner, though <hiex not cause, its return 

 journey to the bottom from which it started. 



