!34 DYNAMICS OF LIVING MATTER 



sufficed for this purpose to add from 30 to 60 c.c. of fresh water to 100 

 c.c. of sea water. If, however, the concentration of the sea water was 

 raised through the addition of i gr. NaCl, or the equivalent amount 

 of some other salt, or of sugar, the animals became positively helio- 

 tropic. Loss of water on the part of the animal acted therefore like cool- 

 ing, and an increase in the amount of water like raising the temperature. 



I made similar observations concerning the changes in the sense 

 of heliotropism in Copepods. 



In some forms light itself seems to play a role in the sense of helio- 

 tropism. The Nauplii of Salami's are positively heliotropic upon 

 leaving the egg, but they soon become negatively heliotropic. Groom 

 and I found that when the larvae were kept in a dark room which was 

 illuminated by a gas flame, they remained positively heliotropic toward 

 the flame. In strong light they soon became negatively heliotropic, 

 and, as a rule, the quicker the stronger the light.* These experiments 

 were made at Naples. Experiments which I made on Nauplii of 

 Balanus in Berkeley showed that the reaction of these latter toward 

 light differs somewhat from those found at Naples, and is much more 

 complicated. 



While in all these cases one would naturally suspect that chemical 

 influences determine the sense and precision of heliotropic reactions 

 of animals, the same is not so obvious in the following cases. Miss 

 Towle found that Cypridopsis, an Ostracode, is at times negatively, 

 at other times positively, heliotropic. The artificial transformation of 

 positively heliotropic specimens into negatively heliotropic was not pos- 

 sible. It was, however, possible to make negatively heliotropic speci- 

 mens positively heliotropic by mechanical agitation. f S. J. Holmes 

 observed that terrestrial Amphipods are positively heliotropic, while 

 the Amphipods living in the water are negatively heliotropic. This 

 led him to try whether or not terrestrial Amphipods would become 

 negatively heliotropic when thrown into water. He found, indeed, that 

 one of these terrestrial Amphipods, Orchesiia, when thrown into the 

 water, becomes rapidly negatively heliotropic. In sea water these 

 animals remain permanently negatively heliotropic, while in fresh 

 water they become positively heliotropic again before they die.J 



I have often wondered whether there are any differences in the be- 

 havior of negatively and positively heliotropic animals aside from their 

 behavior toward light. When larvae of Polygordius were kept in a ver- 

 tical test-tube in a dark room, it often happened that one lot of these 



* Groom and Loeb, Biologisches Centralblatt, Vol. 10, p. 169, 1890. 

 t E. W. Towle, Am. Jour. Physiology, Vol. 3, p. 345, 1900. 

 j S. J. Holmes, Am. Jour. Physiology, Vol. 5, p. 211, 1901. 



