386 University of California Publications in Zoology [Vol. 16 



the responses were positive. Isolated animals have been kept dnring 

 the summer for as long as three days and tested twice a day; yet 

 they are always positive. I have not tried to keep animals so long 

 at the lower temperatures, but there is no change in the responses in 

 seven hours. 



Claitsi reacts similarly to tonsa at the higher temperatures; this 

 is shown in table 1, and other data agree. But at temperatures below 

 15° C the responses of clausi are changed noticeably if the animals 

 are kept too long in the laboratory. There is a summarj^ in table 2 

 tliat will bring this out. 



TABLE 2 



Females of A. clausi from the Surface 



Response to light from window 1 metre away, as affected by laboratory condi- 

 tions; distance and time taken from center to circumference of 16 cm. circle; 

 temperatures 1.5° C or less. 



The table may be said to be .self-explanatory and the effect of 

 laboratory conditions, whatever they are, is evident. No records that 

 enter into table 2 were used in table 1, yet the two tables show similar 

 results so far as claiisi is concerned. 



The effect of the laboratory is correlative with the third of tlie 

 factors under discussion. These two can hardly be separated in 

 practice, but they may be for the sake of discussion. 



3. Influence of Habitat (Environment) prom which Animals 

 ARE Taken 



This influence has been noted by some observers, but not in the case 

 of plankton animals, so far as I know. A recent note by Kepner and 

 Taliaferro (1915) is along this line, as are the interesting observations 

 of Hargitt (1909) on tubicolous annelids. Allee (1912, 1913) has 

 shown that individuals of the same species of isopod, some from a 

 pond and some from a stream, have different sorts of behavior. And 

 Shelf ord (1914) has found that, in comparing the behavior of differ- 

 ent kinds of stream and pond animals, as groups they are contrasted 

 with each other; but within a group there are certain characteristics 

 in common. 



These instances, however, all relate to animals that are permanent 

 residents of any particular habitat. Yet, under certain circumstances, 



