BEHAVIOR OF LOWER INVERTEBRATES 397 



to the degree of angular deviation from a direct course towards 

 the light. 



Besides giving a general account of the reactions of the cray- 

 fish to olfactory stimuli, the paper by Holmes and Homuth •" 

 contains a record of experiments on the effect of the removal 

 of the antennae and antennules and the destruction of the brain. 

 Removal of the outer ramus of the antennules, which bears 

 the so-called olfactory clubs, was followed by a much greater 

 loss of sensitiveness to olfactory stimuli than was produced 

 by the removal of the inner ramus or the large antennae. 

 Specimens with the inner ramus removed react less promptly 

 than normal animals. In specimens with the brain destroyed, 

 the small chelipeds and mouth parts showed a response to meat 

 juice by the usual feeding movements. Various parts of the 

 body were found sensitive to olfactory stimuli, but the region 

 of greatest sensitiveness is the outer ramus of the antennules. 



A study has been made b}^ Hurwitz ^^ of the reactions of 

 earthworms to equimolecular solutions of various acids, and 

 the conclusion was reached that the reactions are due to the 

 hydrogen ions. While in general the reaction times were found 

 to be proportional to the number of hydrogen ions in the 

 solution, acetic acid was shown to have a greater stimulating 

 power than its degree of dissociation would lead one to expect. 



Jackson •*« finds that Hyalellas, which are ordinarily nega- 

 tively phototactic, may be rendered positive by various chem- 

 icals. Acids, alkalis, and various other chemicals were employed, 

 and it was found that there was apparently no relation between 

 the class of chemical employed and the change of response. 

 In order to test the suggestion that the change might be caused 

 by chemical changes produced in the tissues, rather than by 

 the direct stimulating effect of the chemicals used, the exper- 

 iment was tried of very slowly increasing the amount of chemical 

 in the water in which the animals were placed. It was found 

 that it required a considerably stronger solution to cause the 

 change of response than was necessary if the Hyalellas were 

 dropped directly into the solution. On the theory that the 

 reversal is due to the chemical changes in the tissues, the reverse 

 of this relation would be expected. 



Jennings's paper " is devoted to a discussion of the method 

 of applying the principles of physics and chemistry directly 



