388 Universiti/ of Califoriua Publications in Zoology [Vol.16 



In table 4 is brought out the fact that the animals from below 

 the surface are overwhelmingly negative to light if they are tested 

 soon after collection. This is in sharp contrast to the behavior of 

 surface animals at any time. On the other hand, if the subsurface 

 forms remain in the laboratory too long, the reaction is reversed. The 

 second line of table 4 contains the records of five males and five 

 females from a collection in which every animal tested was negative 

 on the preceding day. On that day the animals moved away from 

 the light when released one by one, and they remained on the room 

 side of the stock dish. It is worth noting that the proportion of nega- 

 tive trips is greater at higher temperatures (see note 1), though it 

 is at higher temperatures that surface animals are all positive. 



It is evident that animals kept beyond a certain length of time 

 in the laboratory do not give responses that will help in reaching the 

 true explanation of their behavior under natural conditions. Experi- 

 ments with such material are more likely to mislead us than to further 

 our knowledge of habits. In addition to determining what effect 

 confinement in the laboratory has, it is also necessary that experi- 

 mental animals be obtained from as many different habitats as pos- 

 sible. It can not be said how general the influence of environment 

 on reaction is but this influence should always be ascertained if 

 possible. 



The importance of negative phototropism in Acartia tonsa may 

 be more appreciated if a summarj- of still other data is given. When 

 the source of light is a Mazda lamp, surface animals are always posi- 

 tive, whether it is a 100-watt 19 cm. from the center of the circle, 

 or a 15-watt at a distance of 32 cm. The response is positive no 

 matter what the preceding intensity of illumination may have been. 

 At temperatures of 15°-16° there were no negative trips in 202 

 trials, whether intense light preceded weaker or vice versa, or whether 

 the animals were in the dark previous to testing. It is not fully 

 established whether freshly caught animals from below the surface 

 would be negative to all intensities. A few, however, were negative 

 to the 15-watt lamp under conditions when all others have been 

 positive. 



The preponderance of positive reactions under most circumstances 

 emphasizes the conditions under which negative responses appear, 

 and it is important to note that, so far as the experimenter is con- 

 cerned, these conditions are resident in the animals. 



Another indication of the influence of habitat on reaction mav 



