442 H. p. KJEESCHOW AGERSBORG 



tracts and the organism becomes restive. Complete contraction 

 of the hood is effected by introducing the rod within the area of 

 the hood. WTien a crustacean, ca. 10 mm, or more (I got it to 

 take two Amphipoda, a Cammarus ca. 15 mm. long andaCaprella 

 ca. 20 mm.) is dropped within the rim of the hood, it closes up 

 the hood firmly (fig. 2) without contracting the tentacles on the 

 back of the hood, opens the mouth (while the hood is yet con- 

 tracted), and passes the food into the digestive tract. It also 

 ate a strip of cucumarian muscle ca. 60 cu. mm. but its favorite 

 food seems to be Crustacea (Kjerschow Agersborg, '21). Its 

 favorite position is on the surface film with the back inverted. 

 The cirrhi seems to be receptors of tactile stimuli. The animal 

 may try to swallow anything that comes within the rim of the 

 hood, but it does not swallow everything; it actually tries to 

 eject soUds which have come within the rim of the hood and which 

 it cares not to eat. In life an inner axial white rod is seen through 

 the wall of the cirrhic cone. This axial rod, as I have shown be- 

 fore ('22, in press), consists of nervous tissue; fine fibers radiate 

 from it to the periphery. The dorsal tentacles are not more sen- 

 sitive to tactile stimuli than are the cirrhi. But when they are 

 touched with a glass rod they contract within the sheath of their 

 stalk and remain contracted for a short time. 



SUMMARY 



1. Hermissenda opalescens Cooper responds to tactile stimuh 

 applied to any part of the body ; the head, the oral and dorsal 

 tentacles, the body, the various parts of the foot, and the papillae. 

 The dorsal tentacles give the most effective response to a tactile 

 stimulus, such as the end of a glass rod. 



2. The head and the dorsal tentacles are most sensitive to acids; 

 but of the two, the latter are more sensitive to acids and salts in 

 solution, the tips giving the most effective response. 



3. The oral tentacles are almost as sensitive to stimuli as are 

 the dorsal tentacles, but in addition to a general response of this 

 nature, the oral tentacles also have a selective function in that 

 when they are stimulated by some palatable food, the animal 

 may be made to move in the direction of the stimulus; if the 



