482 



Mr. G. J. Romanes on the 



[Jan. 11, 



radial; or, perhaps still more correctly, that the stimulus escapes from 

 the severed to the unsevered radial connexions through the ricarious 

 action of the latter. I therefore next tested the degree in which these 

 connexions might be cut \\dthout causing destruction of that physio- 

 logical harmony of a lower order which it is their function to maintain. 

 I found that this degree varied considerably in different specimens, but 

 that in no case did the physiological harmony continue after a spiral 

 section had been carried more than once rouud the circumference of the 

 nectocalyx. In these experiments, moreover, I observed that the tracts 

 occupied by the four radial tubes are tracts of comparatively high irrita- 

 bility as regards the manubrium ; for the certainty and ^dgour with which 

 the random motions of the manubrium occur in response to irritation of 

 the part of a nutrient tube contained in a spiral strip, contrast 

 strongly with the uncertainty and feebleness with which these move- 

 ments occur in response to irritation of any other part of such a strip. 

 Lastly, when a spiral section is carried only three fourths of the way 

 round the nectocalyx, so as to leave one of the four radial tubes intact, 

 I observed that, on irritating any part of the strip, the manubrium usually 

 pointed to the single radial tube which still remained intact. JNTow all 

 these facts together, as well as others which cannot be detailed in this 

 abstract, tend strongly in favour of the plexus theory — the radial tubes 

 being supposed here, as in the case of Sarsia, to coincide in their 

 course ^ith that of aggregations of nervous elements analogous to 

 nerve-trunks *. 



§ 4. Character of the Excitahle Tissues of Staurophora laciniata. — In 

 my former paper I described certain spasmodic movements which are 

 performed by StauroiDliora laciniata. The remarkable points concerniug 

 these movements are, that they never occur except in response to stimu- 

 lation, and that, in this particular species at any rate, the_v usually occur 

 only when either the margin of the nectocalyx or one of the four radial 

 tubes are stimulated — stimulation of the general contractile tissue being 

 followed by an ordinary locomotor contraction. Nevertheless stimula- 

 tion of the general contractile tissue a couple of millimetres from the 

 margin is followed by a local spasmodic contraction ; while if the 

 stimulus be applied within a single millimetre of the margin, the effect 

 is a general spasm. Cutting the whole nectocalyx of Staurophora laci- 

 niata into a spiral strip does not in any degree prevent this spasmodic 

 action ; for on irritating the marginal tissue at one end of the strip, a 

 w-ave of spasmodic contraction passes along the entire strip. Such a 

 spasmodic wave has a much greater power of penetration than has an 

 ordinary contractile wave ; for while the latter, in this species, may be 

 very easily blocked by section, the former will continue to pass in spite 

 of the severest forms of section which it is possible to make. Now it 



* Tlie plexus tlieoiy does not suppose anything resembling nerTe-fibres to be present, 

 but merely tracts of functionally differentiated tissue. 



