PHYSIOLOGY: W. E. CARREY 
605 
Palcemonetes when the constant current is passed through the body 
from side to side, and by Ranatra when illuminated from one side. 
The figures of the authors referred to above in this connection will 
serve for illustration of the conditions resulting from our experiments. 
All of the muscular conditions upon which the resting postures are 
dependent are accentuated by activity. The robber flies move in 
circles by farther flexing the legs on the side of the functioning eye and 
extending those on the side of the blackened eye. The head bends 
farther toward the center of the circle and the abdomen curves so that 
the body is concave, forming an arc of the circle in which movement is 
executed. • 
2. Illuminating one eye. Bringing one eye of Proctacanthus into the 
bright beam of light directed through the objective of the optical sys- 
tem of the string galvanometer, while the other eye is illuminated only 
by the subdued light of the optical room, promptly produced the same 
postural relations described in the previous section. In this case the 
diffusely illuminated eye corresponds to the blackened eye. The result 
is due simply to a difference in the intensity of illumination of the two 
eyes. Mast^ has produced similar tonus differences by reflecting light 
from a small mirror on one of the eye spots of Arenicola larvae; the body 
•musculature contracted on the brightly illuminated side. This observa- 
tion we have repeated and noted further that the contracted state per- 
sists as long as the Hght is held on the eye spot. The same curvatures 
have been noted by us when the constant current is passed transversely 
through the body of the marine worm Podarke and have also been de- 
scribed by Moore and Kellogg for the earthworm.^ The general 
mechanism is the same for the action of light and the galvanic current. 
3. Blackening the lower half of both eyes equally results in a symmet- 
rical position of the legs of the two sides but the anterior and middle 
pair are extended forward to the maximal extent, producing a striking 
posture in which the anterior end of the robber fly is pushed up and 
back from the surface of the table. The front pair of legs may even be 
poised up in the air. The body is in opisthotonus with the abdomen 
concave on the dorsal side, while the head is tilted far up and back on 
the long axis of the body. The whole posture is that assumed by 
Ambly stoma or by Palcemonetes as described above, when subjected to 
the influence of the constant current with the cathode at the anterior end. 
Holmes showed similar postures for Ranatra with a light placed above 
and posterior to the animal. 
When walking these robber flies gave the impression of tr3dng to climb 
up into the air. The wings are frequently somewhat spread and the 
