228 HELEN WOODBRTDGE. 



Other Responses. In addition to these responses of a type 

 commonly studied, the larvae showed a reaction of another sort 

 which appears to be of significance in relation to its habitat. 

 One phase of this reaction, the response of turning abruptly 

 upward when stimulated by a passing shadow, has been mentioned 

 in the paper by Dr. Grave and myself. It was found on further 

 observation that this abrupt upward turn occurred not only 

 when the larva was stimulated by a passing shadow, but that it 

 is a common response at other times also. As has been pre- 

 viously noted, the larva does not swim continually, but passes 

 thru alternating periods of activity when it swims vigorously, 

 and inactivity, during which it sinks, motionless thru the water. 

 The behavior of one hundred larvae on resuming activity after a 

 period of quiescense was noted and recorded. Nineteen of the 

 larvae on resuming activity swam downward, seventeen swam in 

 a horizontal direction, and sixty-four swam upward. These 

 and other similar observations indicate that the larva has a strong 

 tendency to swim upward when stimulated to renewed activity 

 after a period of rest. What determines this response is a 

 separate question. One stimulus, quite evidently, comes from 

 the passing of a shadow; others, in all probability, are internal 



in origin. 



It was noted also that larvae frequently swim upward when 

 they come in contact with a vertical surface. The behavior of 

 one hundred larvae on coming in contact with the vertical wall 

 of the container was noted. Of these, sixteen attached them- 

 selves temporarily to the container at the point of contact; six- 

 teen swam downward ; seven swam in a horizontal direction, and 

 sixty-one swam upward. At another time similar observations 

 were made on the behavior of larvae on coming in contact with 

 a piece of black paper suspended in a perpendicular position in 

 the aquarium. Of the hundred cases observed, two ceased ac- 

 tivity and sank; eleven swam along the surface in a horizontal 

 direction, and eighty-seven in an upward direction. These re- 

 sults suggest that the larvae have a tendency to follow surfaces 

 with which they come in contact in an upward direction, par- 

 ticularly if the surface is opaque. 



