392 S. J. HOLMES 



have little influence on the reaction. Increase of concentration 

 by the addition of NaCl or Mg Cl 2 had a strong positivating 

 effect, while hypotonic solutions of these salts produced the 

 opposite result. The action of various stains was tested, but 

 the effects produced were small and of uncertain interpretation. 



Dr. Franz (n) is of the opinion that the role of photo taxis 

 in determining the vertical migration of marine animals is not 

 only unproven but improbable. That fewer animals are caught 

 in a net near the surface during the daytime is attributed to 

 the fact that the animals can see the net better at that time and 

 so escape from being caught. At night they are unable to 

 avoid the net and are hence caught in greater numbers near 

 the surface. 



This conclusion is in part based on the author's conviction 

 that phototaxis is frequently a product of artificial conditions 

 of confinement in a laboratory. Many organisms, according to 

 Franz, react to light in aquaria which do not show any photo- 

 taxis in their natural habitat. Phototaxis is based on move- 

 ments of escape i^Fluehtbewegung), and when it is manifested 

 by animals in nature it is an expression of an effort to get into 

 a free environment or to seek the protection of a secluded nook. 



According to Hadley (12) only well fed lobsters of the fourth 

 .larval stage will respond to light. Hungry individuals do not 

 burrow so readily as those which are well fed, but they are 

 much more active in swimming. Clam juice in the water tends 

 strongly to make the young lobsters swim at the surface, espe- 

 cially if they have been kept without food. 



According to Hargitt (13) there is little relation between the 

 position of the tubes of a number of sedentary annelids (Pro- 

 tula protula, Hydroides pectinata, Potamoceras triqueter and 

 Spirographis spallanzanii) and the direction of the light that 

 habitually falls upon them. In general, Hargitt 's experiments 

 confirm his previous results on these and other tubicolous anne- 

 lids. There is a discussion of the relation of the results secured 

 to the theory of tropisms and the general explanation of animal 

 behavior. 



Harper (14) has carried on experiments to ascertain how the 

 geotropism of Paramecium is affected by teeding the animals 

 with finely divided iron. As the particles accumulate in the 

 posterior end of the body this part tends to sink downward, and 



