Harper, Behavior of Corethra. 443 



different directions, an adaptation which is in accord with the 

 lying-in-wait habit. 



A series of movements A, B, C, D, may be pure overflows of 

 energy, undirected by external agents; E may be directed at food; 

 F may be an avoiding reaction; G, H, I, J, may be again overflow 

 movements. It is seen that A, B, C, D, are random in direction 

 and cause the animal to pomt successively in different ways, which, 

 it may be surmised, has importance at least in the search for food. 

 E and F on the other hand, are directed by external stimuli and 

 are characterized by their definiteness and even precision. The 

 trial and error principle cannot be recognized in such a series for 

 the reason that the fundamental assumptions of the trial and error 

 scheme do not hold. The random movements A, B, C, D are not 

 made under external stimulation. The orientation in the move- 

 ments E and F is not accidental, but immediate and directed. 



REACTION TO MECHANICAL STIMULI AND VIBRATIONS. 



The sensory apparatus of the larvae is highly specialized. Ani- 

 mals which make continuous movements through the water have 

 some sort of feelers located at the anterior end. Corethra in 

 accordance with its discontinuous movements and lying-in-wait 

 habit has no such feelers, but is armed from front to back with 

 sensory bristles. It indeed bristles with warning organs which 

 notify it of the slightest disturbance in the water. It is scarcely 

 possible to bring a glass rod near it without causing it to move. 



Very similar in point of utility are the chordotonal organs of 

 simple nature which respond to vibrations.^ One of the most 

 striking responses of these organisms is produced by tapping an 

 aquarium full of them. Like electric needles they instantly 

 become deflected and usually oriented with the head away from 

 the source of vibration. The response is a single lashing move- 

 ment so directed that the heads of all point in a general direction 

 away from the source of disturbance. This can be repeated 

 again and again at short intervals. This negative response might 

 be surmised to serve to notify of the approach of prey as well as 

 of danger. In catching food, the prey is seized at close range by 



'The chordotonal organs of Corethra are figured in numerous texts, taken from Graber ('82). 

 They can be seen with diagrammatic clearness in the living specimens, or by adding i per cent 

 acetic methyl green. The anatomy of the sensory bristles was worked out by Leydig ('51). 



