No. 4.] AMPHITHOE LONG I MAN A SMITH. \ 79 



contact with the food itself, even when the animal is excited by 

 the presence of food in its vicinity. The darting forth, there- 

 fore, is apparently caused, not merely by a tactile stimulation, 

 but by a chemical stimulus from the food. The antennae are 

 delicate tactile organs, and tactile stimuli may assist in calling 

 forth the actions which result in the seizing of food, but tactile 

 stimulation alone generally fails to accomplish this result. 



After Amphithoe has made a meal of fleshy diet it becomes 

 quite indifferent to the presence of that kind of food in its 

 vicinity and no longer darts forth to grab bits of flesh brought 

 in contact with its antennules. Different individuals present 

 very different degrees of eagerness for animal food, owing 

 doubtless to varying intervals of time since their last repast. 



Sight has probably little to do with the food reactions of the 

 animal. When the head is completely withdrawn in the nest 

 the animals often give signs of perceiving food and dart after 

 it when brought in contact with the antennules. In many 

 cases the nest is so opaque that the animal cannot see through 

 it with any distinctness, and under these circumstances, when 

 the head was entirely withdrawn into the nest, I have often 

 brought bits of meat so they would be touched by the anten- 

 nules only when they were strongly bent backwards. Although 

 the meat was out of sight, the amphipod would dart out, bend 

 backwards, and seize the morsel. If the desired object is out 

 of reach of the antennules, the amphipod will not spring for it, 

 although it may be seen to make ready to do so. It will not 

 go to the length of leaving the nest to seize food, even if its 

 conduct betrays evidence of keen hunger. An object near 

 enough to be struck by the swaying of the antennules is suffi- 

 ciently near to be seized by the animal without letting go its 

 hold of the nest. It is a noticeable feature of the species of 

 Amphithoe and related genera that the antennules are, roughly 

 speaking, of about the length of the body. This feature is not 

 improbably correlated with the similar tube-dwelling habits of 

 these forms, the length of the antennules gauging the length 

 of a safe and successful spring. 



The effect of removing the antennules of Amphithoe is 

 greatly to lessen responsiveness to olfactory stimuli. The 



