450 A. M. Banta 



weakest than to the strongest of them. With current No. 5, 

 however, which was probably much below the threshold of stim- 

 ulation for Asellus, Caecidotea showed no sensitiveness except 

 upon the head and the base of the antenna. 



All the tests with currents i and 2 produced extreme responses 

 Caedicotea except those directed upon the flagellum of the an- 

 tenna. The same tests with Asellus produced extreme responses 

 only upon the head and base of the antenna. Current 4 produced 

 five extreme responses in the eight tests upon Caecidotea, while 

 but three tests aroused any response at all from Asellus. Current 

 5 aroused no response whatever from Asellus while Caecidotea 

 showed sensitiveness to stimulation by it upon the head and bases 

 of the antennae. 



Ten pairs of Asellus and Caecidotea were similarly experimented 

 upon. Records of these experiments are summarized in Table 

 IV. 



Thus to stimulation upon the head by current No. i, 7 Asellus 

 were extremely responsive, 3 strongly responsive and none fairly, 

 slightly or not responsive. To currents i, 2, 3, and 4 applied upon 

 the head a total of 16 were extremely responsive, 14 strongly re- 

 sponsive, 6 fairly responsive, i slightly, and 3 not responsive, etc. 



This table shows that to mechanical stimulation by localized 

 currents of water, Caecidotea is decidedly more responsive than 

 Asellus. Out of a total of 320 individual tests made upon 10 

 animals of each of these species, Caecidotea gave 168 extreme re- 

 sponses and 51 failures to respond, while Asellus gave 61 extreme 

 responses and 90 failures to respond. 



The flagella of the antennae are strangely unresponsive to this 

 sort of stimulation and will receive special consideration elsewhere. 

 If for the present they be left out of account, the number of tests 

 followed by no responses in Caecidotea is reduced to 15, though in 

 Asellus it remains at 73, nearly five times as many. 



The difference in sensitiveness is equally marked when the 

 results of tests by the different currents are compared. Caecidotea 

 gave 59, 53, 36, and 20 extreme responses to currents i, 2, 3, and 

 4, respectively, while Asellus gave 32, 23, 6, and o extreme re- 

 sponses to corresponding tests. With the weakest current (No. 



