Reactions of Isopods 4.4."/ 



1. Asellus is decidedly less sensitive than C?ecidotea to me- 

 chanical stimulation by delicate bristles. .^' 



2. The responsiveness of Asellus decreases rapidly with stimu- 

 lation by the more delicate bristles, while Caecidotea was nearl\» 

 as responsive to the finest as to the coarsest bristle used. 



3. The threshold of stimulation for Asellus is much above that 

 for Caecidotea. 



4. The antennules and flagella of the antennae in both species 

 are only slightly sensitive to mechanical stimulation. 



5. The flagella of the antennae are very much more sensitive 

 in Caecidotea than in Asellus, in which they are scarcely sensitive 

 at all. 



//. With Localized Currents of Water 



A second kind of test for the sensitiveness of Asellus and Cae- 

 cidotea to mechanical stimulation was made by using locahzed 

 currents of water. Fine glass tubes of various calibers were used 

 through which delicate but constant currents of water were 

 carefully directed upon the various parts of the animals. This 

 afforded an easily controlable means of testing sensitiveness to 

 mechanical stimulation. 



The animals, as before, were placed in small wax-bottomed glass 

 dishes containing water to a depth of 2 cm. These small dishes 

 were put into a larger dish of water in which was a thermometer. 

 The water was kept as near il° as possible. A gallon bottle 

 nearly filled with water was placed upon a support on the table so 

 that the water level within the bottle was about 40 cm. above 

 the level of the top of the table. Water was siphoned from this 

 bottle through a rubber tube, into the free end of which was 

 inserted a short glass tube drawn out to a fine point. The siphon 

 flow^ed with a constant current and the rubber tube permitted the 

 short glass end to be freely moved about, making it possible to 

 direct the current wherever desired. A thermometer was kept 

 suspended in the supply bottle. Water of the proper temperature 



