Behavior of Tubicolous Annelids 163 
whole there was possible a total of 75 reactions. Of this number 
71 positive responses were recorded, with four negative ones, or 
94.5 per cent as compared with the Ioo per cent of A. 
Specimen C was tested as in the former cases, but at intervals 
of 30 seconds, and carried on beyond the fifteen tests of the former, 
with a view to determine at what point any signs of fatigue might 
be detected, or whether it was possible to distinguish any periodic 
recurrence of negative reactions. For twenty-five tests the speci- 
men responded promptly and positively. Following this reaction 
it remained in the tube for a period of exactly five minutes. At 
the end of this period it protruded and was promptly tested as_ 
before. At the eighth test the response was only partial. At the 
seventeenth test it failed to respond, but continued after this to 
react positively up to and including the twenty-ninth. The thir- 
tieth was negative, as was also the thirty-second. The thirty- 
third test was followed by a positive response in which the speci- 
men again remained in the tube for a period of five minutes. On 
emergence the tests were resumed and with the following records: 
The second and sixth responses were only partial withdrawals, 
the tenth and thirteenth tests failed toinduce response; fourteenth, 
partial. ‘The fifteenth, sixteenth, eighteenth, twenty-first, twenty- 
third, twenty-fourth and twenty-fifth were all negative. 
In this series of tests it seems strongly probable that we have 
something quite analogous to fatigue, especially in the final twenty- 
five tests. At any rate some condition had become operative in 
modifying in a marked degree the behavior of C as compared 
with A and B and the earlier ones of C. The fact that the tests 
were applied at very brief intervals, and, moreover, that they were 
long continued, go to strengthen the suggestion of fatigue. It is 
necessary, however, in this connection to point out that fatigue 
as here employed does not necessarily imply exhaustion of the 
bodily musculature of the worm, though this may be in some 
measure involved. But fatigue may be sensory, a condition anal- 
ogous to similar conditions induced by long-continued direction 
of the vision to a given test. ‘This point has been referred to in 
the previous paper* and has also been noted by several earlier 
4 Op. cit., p. 302. 
