78 MICHIGAN ACADEMY OF SCIENCE. 



somewhat surprising in view of the striking results obtained by Tower,' 

 who used methods simikir to those employed in these experiments, [t 

 is probable though, that in the experiments of tliis author suHicient at- 

 tention was not given to the exclusion of heat ctt'ecis. and on this ac- 

 count he obtained results different from ours. 



3. The crustacean Hyallela was stimulated by the strong light to 

 increased activity, but it very soon began to weaken. After having 

 been in the light for oU minutes its movements were much weaker and 

 less in amount than in the case of a normal, unstimulated animal, and 

 its sensitiA'ity to mechanical stimulation was also greatly diminished. 

 There seemed to bo a general lowering of the tonus. Recovery was com- 

 plete in about 40 minutes after removal from the light. 



4. A large specimen of a species of Clepsine was at first stimulated 

 to strong muscular activity in the light. After the light had been act- 

 ing for some time however, the sensitivitj- to mechanical stimulation was 

 so diminished as to be practically lost, and the animal was quiet. Com- 

 plete recovery occurred after removal from the light. 



5. In the case of the nemertean identified as SticJiostoiima asensori' 

 atujii it was found that the animal was stimulated to activity above the 

 normal while in the light. On removal from the light it became quiet and 

 was insensitive to mechanical stimulation. 



6. Specimens of FJijjsa while under the action of the light kept in 

 continuous and rapid movement. The sensitivity to mechanical stimuli 

 was greatly diminished while in the light and after removal. On removal 

 all movement ceased. Complete recovery occurred. 



The general result of these experiments is that certain organisms are 

 stimulated to great activity by intense light; but, at the same time the 

 light has something of a paralyzing effect (reduction of tonus), so that 

 the organism moves more and more slowly as the stimulus continues to 

 act. 



1 Tower, W. li. : Loss of the Ectoderm of Hydra viridis in the Light of a Projection Micro- 

 scope. Amer. Xat. 33 : 505-509. 1899. 



