2IO HARRY BEAL TORREY. 



and Nagel, and as gustatory by Jourdain. Such expressions, how- 

 ever, are essentially psychological, and Loeb ('91) has justly 

 insisted upon the substitution for them of some physiological 

 expression, such as chemical irritability. This power of dis- 

 crimination has been shown by Loeb to reside not only in the 

 tentacles (Nagel, '92), but also in other regions. Actinia cqnina 

 discriminated between crab's flesh and small rolls of paper as 

 definitely after he had removed the tentacles by a transverse 

 cut as before. Parker ('96) demonstrated later that Mctridiuin 

 diantlins reacts in different ways to mechanical and chemical 

 stimuli. 



Actinia cqnina, from Loeb's observations, is so definite in 

 its choices that chemically inert paper pellets were never taken 

 into the mouth. Parker found that Metridium would swallow 

 pieces of white india rubber as well as flesh, though the former 

 were sometimes disgorged before they had passed out of the 

 oesophagus. Since he has shown that the cilia covering the 

 lips of Mctndiiun and beating outward in the absence of chem- 

 ical stimuli, reverse their dominant beat in response to the stim- 

 ulation of meat juices, their behavior when stimulated by ap- 

 parently chemically inert india rubber leaves a doubt as to 

 whether or not they can be reversed by purely mechanical 

 means. There is, however, no doubt of such a reaction in 

 S. daiisi, as will be shown in the course of the following ac- 

 count of my experiments. 



It may be well to begin with the effects of various chemicals. 

 Cane sugar in solutions of various strengths produced no ap- 

 preciable reactions in any part of the polyps on trial. Strong 

 picric acid and 4 per cent, formalin caused the retraction of all 

 the tentacles, indicating stimulation of body muscles. One half 

 per cent, hydrochloric acid caused a general contraction of 

 tentacles. From a knowledge of the behavior of Corymorpha, 

 which, though unable to detect the presence of flesh until 

 touched by it, yet reacts strongly to strong alcohol and acetic 

 acid, I am led to suspect that these substances irritate the 

 polyp in the same way that they irritate one's skin, through the 

 tactile organs merely. 



Crab's muscle, bits of limpet and nnm lid worm were used as 



