BYDROTROPISMS OF FRESH-WATER IXVERTEBRA I 53 



4. Although the matter has not been tested, it should be possi- 

 ble to use it in investigating many marine invertebrates. 



5. This device may be used, not only with creatures with sound 

 vision; but, al>-o, with forms that have been rendered blind by 

 manipulation. 



II. In testing this device several ecological types of inverte- 

 brates were used: those that creep along the bottom of the 

 body of water or along water plants, but do not leave the pond 

 or stream (Ascllns, half grown dragonfly larvae, pond snails 

 [these occasionally venture beyond the water edge]); those 

 that creep along the bottom or up vegetation and occasionally 

 leave the water (crayfish, scavenger beetles); those that live on 

 the film and never depart far from it (giant water striders); 

 those that dwell on the film, but migrate from one body of water 

 to another (whirligig beetles). 



1. The movements of neither pond snails, asellids nor dragon- 

 fly larva.' are influenced by nearby bodies of water. 



2. In the majority of cases the movements of crayfish are con- 

 n "lied l>y the nearest body of water. When out of the water 

 they behave as though they arc positively hydrotropic. Blind 



h do not so react; this demonstrates that the movements 

 of this crustacean, when out of the water, are controlled by visual 

 -(iinuli furnished by the nearest body of water. 



3. About half of the scavenger beetles investigated act as 

 though t! ively hydrotropic; the other half are not 

 influenced, in .1 directive manner, by nearby bodies of water. 



4. When on land, the majority of the water striders investi- 

 gated are not influenced, in their movements, by the nearest 

 body of water; a few act as though they are p ly hydro- 

 tropic. 



5. When out of the water, whirligig beetles are undoubtedly 

 influenced, in their movements, by the nearest body of water. 

 On the checkerboard plate the majority always move toward the 

 water; when set at liberty within forty feet of a 1>"<1\ of water, 

 they always fly toward it. If blinded they do not react in this 

 manner. This demonstrates that they are controlled by visual 

 -liinuli furnished by the water. 



6. This paper does not contend that the-e movements which 

 .-nine of the forms make towanl watt r are po-itive hyclrotropisms 



