462 G. H. PARKER 



best, the animal commonly envelops itself in a mucous coat, 

 which is often sloughed and forms a loose tube about its base. 

 This secretion of mucus, which occurs in response to a great 

 variety of stimuli, mostly noxious, is undoubtedly a means of 

 protection, as has been suggested by Duerden ('06) and by Gee 

 ('13), and recalls the more permanent secretions of such actinians 

 as the cereanthids, in which protective tubes are regularly pro- 

 duced. 



But mucus is not only discharged in response to noxious 

 stimuli; it is also produced through the action of favorable 

 influences. Meat juices call forth, especially from the tentacles, 

 a profuse discharge of mucus which renders these organs extremely 

 sticky. In this way the capture of food is greatly facilitated. 



After Metridium has been submerged in fresh water for a 

 brief period the mucus discharged on its oral disc is not usually 

 simply sloughed off but much of it may be swallowed as it is 

 in such corals as Favia and Fungia where, according to Duerden 

 ('06), the chief means of feeding is by swallowing the mucus of 

 the oral disc in which small organic fragments, etc., have been 

 entangled. This method of feeding is not known among the 

 actinians, but the response of Metridium just described shows 

 how easily the actinian method of capturing food could be 

 converted into that employed by Favia and Fungia. 



If a given spot on the outer surface of the column of Metri- 

 dium is touched three or four times with the end of a small, 

 blunt glass-rod, a slight clot of milky mucus will soon appear. 

 This clot is to be seen in the exact region of stimulation and 

 though this region often shows a considerable depression due 

 to muscular contraction which may spread horizontally half 

 way round the column, the secretion of mucus always remains 

 strictly localized and gives no evidence of being extended through 

 muscle contraction or nerve transmission. 



Dilute acids and dilute alkalies also bring about a free dis- 

 charge of mucus. Juice from the meat of the killifish, Fundu- 

 lus, when applied to the isolated tentacles or acontia likewise 

 produces a free discharge of mucus. The discharge of mucus 

 on the acontia forms a tube through which this organ gradually 

 makes its way by ciliary action. 



