88 G. H. PARKER 



From all the regions named in the preceding statements — and 

 these regions together represent practically the whole outer sur- 

 face of the actinian — the retraction of the oral disc could be 

 called forth by mechanical stimulation of varying degrees of in- 

 tensity. It will be recalled that, according to the scheme of nerv- 

 ous transmission in actinians proposed by the Hertwigs ('79- 

 80), a scheme based exclusively on histological evidence, im- 

 pulses from the ectoderm of the animal were supposed to pass to 

 the oral disc, thence down the ectoderm of the esophagus to 

 the mesenteric filaments and thus to the entodermic musculature, 

 such as the longitudinal muscles of the mesenteries. To ascer- 

 tain the course of these impulses as tested physiologically, a 

 series of observations were made on actinians that had previ- 

 ously been subjected to operations designed to interrupt certain 

 possible courses. 



1. If the wall of the column of Metridium is cut through in a 

 complete ring equatorially, that is, the column is girdled, a me- 

 chanical stimulus applied either to the oral portion of the column 

 wall or to the pedal portion will call forth a general retraction 

 of the oral disc. 



2. If the whole oral disc is cut off, a mechanical stimulus ap- 

 plied near the former equator or, better, near the pedal edge, is 

 followed by a contraction of such parts of the longitudinal mesen- 

 teric muscles as remain in the preparation. This experiment con- 

 firms the statements made by Jordan ('08) that the oral disc is 

 not necessary for the activity of the longitudinal mesenteric mus- 

 cles, and it shows that, contrary to the opinion held by the Hert- 

 wigs ('79-80), there are direct transmission paths from ecto- 

 dermic sense cells to entodermic muscles independent of the 

 esophagus. Histological evidence of such paths has already 

 been advanced by von Heider ('77, '79, '95), Havet ('01) and 

 Parker and Titus ('16). 



3. If a tongue of the column wall is cut from the pedal edge of 

 the column up to its equatorial region and there left in organic 

 connections with the rest of the animal (fig. 1) and a mechanical 

 stimulus is applied to the free end of the tongue (X) , a response 

 of the whole system of longitudinal mesenteric muscles follows. 



