HYDBOIDS 187 



its foot-end and its hydranth projected for some distance 

 horizontally and freely into the surrounding water. On 

 applying a faradic current to the hydranth, the foot-end 

 contracted together with the rest of the stalk ; on apply- 

 ing it to the foot-end, the hydranth contracted together 

 with the rest of the stalk. The polyp was now unpinned, 

 bent into the shape of a U with the curve where the pin 

 had been and this part was dipped for from one to two 

 seconds into ten per cent, acetic acid and then immedi- 

 ately immersed in pure seawater. As a result of this 

 treatment the ectoderm was killed in a broad ring around 

 the middle of the stalk, but the deeper tissues, at least the 

 axial vacuolated cells, were left alive. On pinning the 

 polyp again in the horizontal position and stimulating it 

 electrically, it was found that the nervous impulse never 

 passed from one end to the other, as in the first trials, 

 but was always limited to the end at which it was applied, 

 showing that the superficial tissue of the polyp, but not 

 its core, is the part concerned with transmission. 



This experiment was repeated with the modification 

 that, instead of destroying the superficial tissue with 

 acetic acid, it was anesthetized with chloretone. Polyps 

 thus treated failed to transmit impulses over the anes- 

 thetized region, though after ten minutes in pure sea- 

 water transmission in this region was reestablished. As 

 chloretone is known to* abolish the neuromuscular activ- 

 ities of the ectoderm, but to leave the entodermic muscles 

 unaffected, it was concluded that the parts concerned 

 with transmission are not only superficial but ectodermic. 



To determine whether there are special transmission 

 tracts in the polyp, several lines of experimentation were 

 carried out. A large polyp was split lengthwise from the 

 hydranth end through the column almost to the aboral 



