MECHANISM IN SEA-ANEMONES. 341 



entoderm and the two parts thus estabhshed are beUeved by many 

 investigators to be continuous in the oesophageal region where ecto- 

 derm and entoderm are confluent. According to O. and R. Hertwig 

 (1879-1880), Wolft" (1904), and others this nervous network is 

 more extensively developed in the oral disc than elsewhere and 

 constitutes there a primitive central nervous organ. Groselj (1909), 

 however, believes that this centralization is in the oesophagus. Many 

 other workers (Nagel, 1892; Loeb, 1895; Parker, 1896. Havet, 

 1901 ; Bethe, 1903; Jordan, 1908, 1912) maintain that this network 

 is not sufficiently centralized anywhere in the actinian's body to 

 justify the statement that the nervous system of the sea-anemone is 

 other than a diffuse one. 



X'igorous stimulation of almost any part of the surface of a 

 sea-anemone is commonly and quickly followed by the complete 

 contraction of the whole animal ; and the response is so protracted 

 that actinian muscle has come to be regarded as specially adapted 

 to tonic contraction rather than to the rapidly changing phases of 

 contraction and relaxation so characteristic of the muscles of the 

 higher animals. This view has gained such strength that von 

 Uexkiill (1909) and Jordan (1909, 1908, 1912) have come to look 

 on these muscles as almost exclusively tonus muscles and Jordan 

 (1908) especially has gone so far as to deny to sea-anemones the 

 possibility of muscular reflexes such as are so usual among the 

 more differentiated animals. An adequate examination of the 

 muscular activities of sea-anemones will show, I believe, that these 

 animals have a much more complex muscular mechanism than has 

 been previously suspected and that at least three and possibly four 

 types of muscular activity can be distinguished in them. 



The simplest of these types is that seen in the longitudinal muscle 

 of the acontium. This muscle can be brought into action by the 

 direct application of an appropriate mechanical or chemical stimulus. 

 Its contraction changes the acontium from a long straight filament 

 into a loosely twisted, spiral one. This response is strictly local in 

 relation to the stimulus and does not spread appreciably from the 

 region stimulated to other parts. It is as well pronounced in acontia 

 that have been in an anesthetizing solution (magnesium sulphate or 

 chloretone) long enough to abolish all nervous activity in other parts 



