476 G. H. PARKER 



mechanically stimulated, this organ responds by turning eventu- 

 ally toward the mouth of the animal, after which it gradually 

 assumes its initial position. The movements thus induced are 

 in the beginning without doubt due entirely to the activity of 

 the longitudinal muscle but before long both longitudinal and 

 circular muscles are certainly involved for, though there may 

 be no nervous connection between them, their physical relations 

 are so intimate that the activity of the longitudinal fibers may 

 perfectly well serve as a mechanical stimulus to call into action 

 the ■ circular system. In this instance then, the longitudinal 

 muscle of the tentacle may act independently in the beginning, 

 but it is quickly followed by its natural opponent, the circular 

 muscle. 



If the tip of a tentacle in Metridium is cut off, the tentacle 

 contracts, the wound almost at once closes with a nipple-like 

 formation, and the tentacle with its tip firmly puckered gradu- 

 ally reexpands. In this condition it remains until the injured 

 end is fully healed (Chester, '12). At the beginning of this 

 operation, during which the tentacle is contracted, the longi- 

 tudinal as well as the circular muscles are involved, but after 

 the tentacle has reexpanded and before the wound has healed, 

 a matter of a day or so, the circular fibers near the cut are the 

 only muscular elements really active. Thus the circular muscle 

 as well as the longitudinal may under particular circumstances 

 give evidence of independent action. 



The transverse muscles of the mesenteries. These muscles 

 connect the column wall with the oesophagus. If a small amount 

 of sea water is discharged into the mouth of an expanded, resting 

 Metridium no response is usually noticeable. If the seawater 

 is a ^ hydrochloric acid solution, the actinian immediately 

 opens the oesophagus widely and exhibits on its column a few 

 well marked vertical grooves. These disappear gradually as 

 the oesophagus closes. If the position of these grooves is care- 

 fully noted, it will be found that one is always present for each 

 siphonoglyph and that the others are distributed in accordance 

 with the arrangement of the other pairs of complete mesenteries. 

 The grooves thus mark the lines of attachment of these mesen- 



