NERVOUS SYSTEM OF THE TUNICATE 311 



of the animals no reactions were observed, while for the other 

 frequent contractions were noticed, especially of the atrial 

 siphon. This siphon proved to contain one or two parasitic 

 Crustacea, 3 to 4 mm. long, partially embedded in the siphon 

 near its tip, and whenever they kicked up a rumpus the siphon 

 closed, and the closing of this siphon often induced closure of 

 the other. The parasitized atrial siphon being in a quasi con- 

 tinuous state of irritation responded more readily to the vibra- 

 tions in the room than did the unexcited siphon. Sometimes 

 small crabs were found living symbiotically in the pharyngeal 

 sacs of the tunicates, 



B. Responses to tactile stimulation 



To penciling with a bristle the siphons give local responses, 

 thus only the lip-lobe on the stimulated side of the siphon 

 puckers in, provided that the stimulus is feeble; to a stronger 

 stimulus, however, all lobes of the stimulated siphon respond, 

 and if the penciling be of sufficient strength, the closure of the 

 incurrent siphon is followed by closure of the excurrent siphon 

 as well. 



The base and body of the animal are insensitive to penciling, 

 while the necks of the siphons are slightly sensitive, though less 

 so than the lip-lobes. The margins of the two siphons are there- 

 fore the most sensitive areas of the entire body. As to relative 

 responsiveness, little difference could be discovered between oral 

 and aboral siphons; in one or two cases the aboral or excurrent 

 siphon was the more sensitive of the two. 



EFFECT OF OPERATIONS UPON THE TACTILE RESPONSE 



A. Slitting the siphons 



When the oral siphon was slit lengthwise for half an inch, 

 cleaving it in two parts, and the lobes of one side were stimulated, 

 there was a response first in that half, then after a second's 

 latent period a response in the other half. A reversal of the 



