42 University of California Publications in Zoology [Vol. 19 



back against the body. There is another sort of movement, however, 

 that is so slow it is barely perceptible. It is brought about by very 

 gentle motion of the feet, some of the head appendages, and the abdo- 

 men. If the word "wiggle" may be used it serves to describe the 

 action of the appendages. One is aware that there is a slow change 

 of position, but it gives the impression of "creeping" or "drifting" 

 as I have called it for myself. There are times, also, when none of 

 the appendages are in motion, and then the body assumes almost any 

 posture in the water ; the head may be down or up, or the body tilted 

 toward one side, so that a line passed through the extended antennae is 

 neither horizontal nor vertical. It has seemed to me that the drop 

 of oil in the body has something to do with the position taken ; there 

 is a tendency for the posterior end to gradually rise higher than the 

 anterior end, and the oil drop is always nearer the posterior end. 

 I believe that the "creeping" movement is due to the action of the 

 appendages ; I have not been able to determine that there is any change 

 of position unless the appendages are moved. When an animal is 

 in a vertical tube the ' ' creeping ' ' produces either ascent or descent. 



If a specimen is in a shallow dish it can be gently moved about 

 with a capillary rod so that the axis of the* body takes any desired 

 direction as regards the light. Under such circumstances one can 

 easily see how the creeping will alter the position of the animal. The 

 appearance is as if the body were drifting in a very gentle current of 

 air over the surface. The animal moves in almost any direction, even 

 sideways, or it swings around through part of a circle. 



It does not seem to me that the so-called creeping movement is in 

 the nature of a response. The direction of such movements is too 

 irregular and aimless. They may lead to ascent or descent, or move- 

 ment toward or away from the light, or in a line parallel to the window. 



PHOTOTROPISM 



Although the drifting is without definite direction, the other sort 

 of locomotion is very definitely negative phototropism. The swooping 

 dash is always away from the light. It takes place without any pre- 

 liminary signs. If the head of the animal is directed toward the light 

 one movement of extraordinary speed turns the body and carries the 

 animal toward the side of the dish opposite the light. This behavior 

 can be best observed in a shallow dish, but in a tube also the actual 

 swimming is away from the light. Table 11 summarizes the results 

 of the experiments; both the l-apid and the slow movements are in- 



