NEUROMUSCULAR MECHANISM IN METRIDIUM 449 



for actinians and more recently b}^ Hickson, Ashworth, and 

 Kiikenthal und Broch for alcyonarians. 



Since from any point on the ectoderm of the lower part of 

 the column the longitudinal muscles of all the mesenteries can 

 be brought into action, it follows that the nem'omuscular mech- 

 anism of the column and adjacent parts must be much more 

 extensive and complex than that of the tentacles. Besides sense 

 cells and muscle cells there are very probably in the parts under 

 consideration intermediate cells which, if not motor cells in 

 the sense of Havet, are at least transmitting cells connecting 

 the sensory mechanism with the motor. If this view is correct 

 the ectodermic sense cells are only indirectly connected with 

 the mesenteric muscles and a system more complex than that 

 in the tentacular ectoderm must be present. 



Wlien a spot on the lower portion of the column in Metridium 

 is stimulated, the response that follows, as already stated, is 

 in the longitudinal muscles of the mesenteries. The circular 

 muscle of the column, though nearer the point of stimulation than 

 the mesenteric muscles, exhibits no obvious acti\dty. Probably 

 its tonus is increased by the contraction of the longitudinal 

 muscles, but of this we have no evidence. If the stimulated 

 spot on the column is now covered with crj^stals of magnesium 

 sulphate, these will dissolve and in a few minutes the whole 

 area will be found to be fully anesthetised. The spot may now 

 be freely touched without calhng forth a contraction of the 

 longitudinal muscles. As a result of such stimulation, however, 

 a horizontal band of contraction soon appears and passes slowly 

 round the column. This constriction is undoubtedly due to 

 the contraction of certain of the circular-muscle fibers in the 

 body wall and since the nervous mechanism of this region has 

 been rendered inoperative by anesthetisation, these fibers must 

 have been stimulated directly. We therefore conclude that 

 while the column wall has nervous connections by which the 

 longitudinal muscles may be brought into action, it also contains 

 muscle fibers that contract in response to direct stimulation. 

 The normal stimulus for these muscles has not been definitely 

 determined, but it is probably the stretching to which they are 



THE JOURNAL OF KXPERIMEXTAL ZOOLOGY, VOL. 21, XO. 4 



