370 MARGARET FLOY WASHBURN 



When full daylight falls suddenly upon it, the body contracts 

 and the tentacles expand and cover it. In dim light it seeks 

 the lightest region. Yellow and red affect the unfolding differ- 

 ently from green and blue. Actinia sulcata drops its tentacles 

 in darkness "as if sleeping." 



Echinoderms. The paper by Cowles (3) is chiefly concerned 

 with the reactions to light and shadow of isolated pedicellariae 

 of the sea-urchin Toxopneustes varicgatus. Von Uexkull has a 

 theory that the reaction of the spines to shadows is due to the 

 release of energy from certain "Tonus" centers in the radial 

 nerve, energy having been stored in these centers by the action 

 of light and being set free when the light is withdrawn. He 

 found that the reaction to shadows did not occur when the 

 connection with the radial nerve was broken. Cowles has ob- 

 served that in the case of the pedicellariae, however, response 

 to shadowing will take place when they are disconnected from 

 the radial nerve. He concludes that their Tonus centers must 

 lie in the tissue of the pedicellariae themselves. 



Annelids. Allolobophora jociidas power of discriminating a 

 wet from a dry surface has been investigated by Parker and 

 Parshley (21). A worm that is creeping over a surface of wet 

 filter paper will, when it comes to a dry spot, after moving 

 over it for a short distance "varying from a few segments to 

 half its length," stop, move its head from side to side, with- 

 draw into the moist area, and take a new direction. When 

 worms were forced to creep backwards into a dry area, they 

 did not show any tendency to check their movements. The 

 authors omit to note that this in itself would not be good evi- 

 dence as to the part of the body which is especially sensitive 

 to dryness, for the worms might have been so occupied with 

 escaping from the stimulation of the head, which was forcing 

 the backward movements, as to be indifferent to dryness. Indi- 

 viduals with the prostomium removed or anesthetized, how- 

 ever, manifested a similar indifference to dryness and it is con- 

 cluded that the prostomium is the organ which responds to 

 dryness as a stimulus. This stimulus probably acts through the 

 extraction of water from the peripheral protoplasm of the worm, 

 concentrating and partially coagulating the body materials in 

 the prostomium. 



