282 STUDIES IN GENERAL PHYSIOLOGY 



of heliotropism upon the temperature and concentration of 

 the sea-water in marine animals which are far removed in 

 the animal scale from the Annelids, namely, Copepods. I 

 worked on a series of Copepods which were always collected 

 by the tow net, a number of which, however, are not yet 

 classified. The species which was found in largest numbers 

 is, according to Dr. Bumpus, probably Temora longicornis. 

 The freshly caught Copepods were not negatively heliotropic 

 at first like the Polygordius larvae, but positively heliotropic ; 

 the majority of these, however, soon became negatively 

 heliotropic. Jarring made them positively heliotropic tem- 

 porarily. They were much less resistant than Polygordius 

 larvae. An increase in temperature made the positively 

 heliotropic Copepods negatively heliotropic, and increased 

 the negativeness of the Copepods already negatively helio- 

 tropic. A lowering of the temperature made the negatively 

 heliotropic Copepods positive and increased the positiveness 

 of the positively heliotropic Copepods. An increase in the 

 concentration of the sea-water increased the positiveness^ 

 and a decrease in concentration increased the negativeness^ 

 of the Copepods. A few examples may serve to illustrate 

 these facts. At +22 C. the Copepods were positively 

 heliotropic. In the course of five minutes the temperature 

 was raised to 26 C., when the majority became negative. 

 I continued to raise the temperature to 32 C., but the ani- 

 mals remained negative. I then cooled the water. The 

 animals became positive when only 20 C. was reached, and 

 remained so while the temperature continued to fall. The 

 change in the temperature seems to be the important circum- 

 stance in Copepods which changes the sense of heliotropism. 

 In another experiment the Copepods were negative at 24 C. 

 I cooled the vessel rapidly so that the temperature fell to 

 21 C.; at this point a part of the animals already became 

 positively heliotropic. At a temperature of 7 C. all had 



