194 University of California Publications. [zoology. 



definite views relative to these possibilities. As to the first two, 

 however, a number of general considerations lead us to doubt 

 their being real factors in the problem. Concerning pressure 

 there would appear to be no good ground for supposing that this 

 species of enteropueust is not, egg, young, and all, like other 

 bottom dwellers, fully adapted to the pressure conditions under 

 which it lives, and consequently would not be influenced by 

 pressure to swim upward. 



As to the possibility of oxygen as a determining factor, the 

 problem presents itself in about the following way : In the first 

 place, the obviously low grade of vital activities of the organism 

 as a whole should be satisfied with a comparatively small supply 

 of oxygen, which should be present at any of the depths here 

 concerned. Iu the second place, the best information we have 

 concerning atmospheric oxygen in sea water is to the effect that 

 its dissemination is very little if at all dependent upon depth in 

 itself, but rather upon secondary, local conditions, such as, for 

 example, the abundance and kind of organisms. This being so, 

 it is hardly to be supposed that there is a sufficiently constant 

 increase of oxygen from the bottom upward, especially in a 

 locality like that with which we have to do, wherein vegetable 

 life and currents are extremely variable, to bring about so con- 

 stant a reaction phenomenon as that of the upward migration of 

 this organism. 



As to the direct effect of temperature on movements, all our 

 laboratory experience points to the conclusion that increase in 

 temperature above that of the water in which the larva? are 

 taken, even by the smallest amounts, tends to retard rather 

 than to accelerate the rate of swimming. On the interesting 

 question of the effect on the movements of plankton organisms 

 wrought by change in viscosity of the water due to change in 

 temperature, we have already presented the little evidence we 

 have, and need consequently only refer the reader to what is 

 there said. 



It seemed so likely that positive phototaxis might play at 

 least a part in inducing the upward movement that we devoted 

 considerable time to experimental studies on the point. As our 

 results were almost without exception negative, it will not be 



