412 H. BOSCHMA. 



their movement. In subsequent papers (Parker, 19050, 1905^) 

 the same author has worked out this phenomenon in further 

 details. He found that certain chemical substances can induce 

 the cilia to reverse. A number of statements on the part of the 

 tentacles and of the ciliary action in different actinians during the 

 feeding reactions is described by Carlgren (1905). This author 

 found that in some species of actinians the ingestion of food takes 

 place chiefly by ciliary action (e.g. in the Protanthea?) ; in other 

 forms, however, the tentacles are the chief organs for the capture 

 and transportation of the food to the mouth (e.g. Tealia). 



The fact that not all the individuals of a certain species of 

 actinian react in the same way on the same stimulus, was demon- 

 strated by Jennings (1905). The state of metabolism of the 

 actinian is one of the most important factors determining the 

 reaction to substances which come into contact with the tentacles 

 or the oral disk. Thus hungry polyps often will ingest inedible 

 matter, while well-fed ones will refuse the same material. Pieron 

 (1906) also states that different individuals of one species behave 

 differently towards the same stimulus. 



Different species of actinians also behave in quite a different 

 way. Some species of actinians in confinement would ingest only 

 a very limited variety of food, e.g. Eloactis, which refused every- 

 thing but living Balanoglossus and Hydroides (Hargitt, 1907). 

 On the other hand many other species ingest besides food also 

 indigestible material. Instances of this are recorded by Torrey 

 (1905) for Sagartia, Fleure and Walton (1907) for Tealia, Parker 

 (1896) and Allabach (1905) for Metridium. In the case of 

 Metridium, Parker (1905), however, has expressed the opinion 

 that the foreign matter (filter paper) was touched by the hands of 

 the experimenter and therefore acted as a chemical stimulus. 

 All of the above-named forms, as also Actinia (cf. van der Ghinst, 

 1906) are able to discern food-particles from inedible matter. 

 The latter is usually refused and food particles are ingested. 



Summarizing the data available in the literature and those of 

 his own investigations Parker (1917) states that the different 

 factors which are combined to bring about the feeding reactions in 

 actinians are the following: secretion of mucus, ciliary action, the 

 action of the neuromuscular apparatus of the tentacle?, of the 



