CHAPTER XI 



APPROPEIATION OF FOOD AND THE 

 NERVE-NET 



IF the ccelenterates, whose nervous system is largely 

 a nerve-net, nevertheless exhibit locally signs of a higher 

 differentiation, may it not be possible that in some of 

 their more complex operations they may show signs of 

 all the higher nervous functions of the most complex 

 animals? In attempting to find an answer to this ques- 

 tion, so far as actinians are concerned, such activities 

 as their feeding habits, their retraction and expansion, 

 and their locomotion have been investigated. 



The appropriation of food is an activity with which 

 the oral disc of actinians is principally concerned. The 

 movements of the tentacles, mouth, and other such parts 

 by which food is ingested were ascribed by Nagel (1892, 

 1894) to muscular action alone, but Loeb (1895) pointed 

 out that cilia also play an important role. The parts that 

 are immediately concerned in the appropriation of food 

 are the five following: the tentacular gland cells, whose 

 secretions render the tentacles adhesive, whereby pieces 

 of food become attached to them ; the musculature of the 

 tentacles, by which these organs are pointed toward the 

 mouth ; the tentacular cilia, which sweep toward the ends 

 of the tentacles and thus deliver the food to the mouth 

 when the tentacles are pointed in that direction; the 

 transverse muscles of the complete mesenteries, by which 

 the oesophagus is opened; and the cilia of the lips and 

 oesophagus, which in the presence of food reverse their 

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