NERVOUS TRANSMISSION 



93 



if a mechanical stimulus is then applied to the column of 

 one half, the portion of the oral disc in that half will be 

 regularly withdrawn while that in the other half will be 

 at most only rarely moved. Hence it follows that the 

 region of the mouth, particularly of the lips, must 

 be regarded as one poor in nervous connections. Conse- 

 quently the view originally advocated by the Hertwigs 

 and later by Wolff (1904) and by Groselj (1909) to the 

 effect that the region of the mouth is the chief region 

 of nervous connection between the ectoderm and 

 entoderm is not supported by direct observation, for, 

 as has just been shown, this region is one poor in its 

 capacity for nervous transmission and, as was shown 

 earlier, there are abundant direct connections between 

 the ectodermic receptors and the entodermic muscles 

 without recourse to such 

 areas as the region of the 

 mouth and the oesophagus. 

 The conducting paths in 

 the nervous organization of 

 a sea-anemone can be dem- 

 onstrated in a variety of 

 ways. If a tongue of tissue 

 is cut equatorially from the 

 column of a sea-anemone 

 so as to girdle it for half 

 its circumference (Fig. 24), 

 and a stimulus is applied to 

 the free end of the tongue, such stimulus is only occa- 

 sionally followed by a retraction of the disc, showing 

 that this least sensitive portion of the column is not in 



FIG. 24. Metridium from which an equa- 

 torial tongue has been cut from the column. 

 Stimulus applied at x. 



