446 A. M: Banta 



only20 and 10 such reactions were obtained. Hence it seems clear 

 that Asellus is much the less responsive of the two species to this 

 form of mechanical stimulation; that its responsiveness decreases 

 rapidly with stimulation by the more delicate bristles; and that 

 the threshold of stimulation is reached by the bristles used, 

 whereas Caecidotea is more responsive to such stimulation; in 

 fact is nearly as responsive to stimulation by the smaller as by 

 the larger bristles; and is extremely responsive beyond the thres- 

 hold of stimulation for Asellus. 



Asellus is more deliberate and less hasty in its reactions to 

 mechanical stimulation than Caecidotea is. This difference in 

 the character of the reactions may influence one's judgment of 

 the vigor of the reactions, so that the vigor of the response of 

 Asellus is underestimated. Consequently a greater number of 

 responses made by the Asellus possibly should be credited to the 

 extreme column, than has been done. But if such an error should 

 exist with reference to the extreme column for Asellus, it cannot 

 affect the general result, as there can be no doubt of the diminu- 

 tion in number and vigor of the responses. Moreover, in many 

 tests the actual lack of reaction in Asellus indicating lack of sensi- 

 tiveness to more delicate stimulation is in strong contrast with the 

 extreme sensitiveness of Caecidotea. 



The flagellum of the antennae and the antennules are- very deli- 

 cate organs. Both are armed with many sensory hairs and might 

 readily be thought highly sensitive to tactile stimulation. The 

 flagella of the antennae are relatively long and m both species, 

 when the animals crawl, these organs extend in advance for a 

 distance equal to more than half the length of the body. They 

 appear to serve as importantorgansof touch. However, it appears 

 that these organs in both species are relatively slightly sensitive 

 to tactile stimulation of the sort employed. A remarkable dif- 

 ference exists between the sensitiveness of the flagella of the anten- 

 nae in the two; in Caecidotea the flagella are only moderately sensi- 

 tive, but in Asellus they are scarcely sensitive at all. 



From the foregoing experiments the following conclusions may 

 be drawn : 



