HABITS AND REACTION'S OF SAGARTIA DAVISI. 215 



their dominant outward beat, and are able to carry away non- 

 stimulating objects. At the end of the period of digestion and 

 absorption, the ingested bodies have reached their minimum of 

 stimulating power ; and now, no longer able to reverse the 

 dominant beat of the cesophageal cilia, they are carried out by 

 the latter just as soon as they come into their sphere of influence. 

 Why chemically inert bodies, once swallowed, should be dis- 

 gorged, may be explained, I believe, by assuming inability on 

 the part of the cesophageal cilia to continue reversing their dom- 

 inant beat in the presence of a persistent or frequently applied 

 mechanical stimulus which was originally weakly positive. This 

 is in entire harmony with Parker's demonstration that after 

 repeated applications of a weak chemical stimulus to the 

 lips of MctriJiuin, there comes a time when no positive reaction 

 results. 



Peristaltic movements of the oesophagus may assist the cilia, 

 but I have no evidence that they take more than a very subordi- 

 nate part in the phenomena of swallowing or disgorgement. 



UNIVERSITY OF CALIFORNIA, 

 January 1 1, 1904. 



