452 A. M. Bant a 



4) 20 extreme responses were given by Caecidotea and only 25 of 

 the tests; 10 of which were upon the flagellum of the antenna, 

 failed to produce any reaction at all. With Asellus the same 

 tests produced no extreme responses, while there were 63 failures 

 to respond out of a total of 80 tests. Hence it appears that 

 Caecidotea is quite responsive to the weakest current used while 

 Asellus is only slightly so. 



The same relative lack of sensitiveness noted in the flagella 

 of the antennae, when stimulated by the bristles, was again noted 

 with the currents. To stimulation by localized currents the fla- 

 gella in both species are rather insensitive. This is especially true 

 with Caecidotea, whose flagella seemed less sensitive to this sort 

 of stimulation than those of Asellus. To stimulation by bristles 

 the reverse was true for in those experiments the flagella of the 

 antennae were more sensitive in Caecidotea than in Asellus. A 

 possible explanation of this discrepancy is that bristles tend to 

 produce vibrations more than currents do and that the flagella 

 are probably quite sensitive to frequent vibrations. This will 

 be taken up again when the discussion of the reactions to sound is 

 reached. The portions of the body of Asellus most sensitive to 

 stimulation by currents are the head and the bases of the anten- 

 nae. They were almost the only parts responsive to the weakest 

 currents. In Caecidotea the maximum sensitiveness is less con- 

 fined to the head and flagella of the antennae than in Asellus, 

 smce it is shared somewhat by the uropods and legs. This point 

 was well brought out by using current 5 with a number of pairs 

 of individuals. Caecidotea was found to be somewhat sensitive 

 to this current upon the head, base of the antennae, uropods and 

 legs, but Asellus was seldom sensitive to it at all and never except 

 occasionally upon the head and bases of the antennae. 



From these experiments upon the eff^ects of mechanical stimu- 

 lation by localized currents of water the following conclusions are 

 drawn : 



1. Caecidotea is much more sensitive to water currents than 

 Asellus. 



2. The sensitiveness of Caecidotea is only a little less marked 



