1876 MEDUSAE 25 



of the radial tubes occurs in the course of the spiral, 

 irritation of that portion causes a much stronger re- 

 sponse on the part of the polypite than does irrita- 

 tion of any of the general bell-tissue, even though 

 this be situated much nearer to the polypite. This 

 seems to show that the nervous plexus, if present, 

 has its constituent fibres aggregated into trunks in 

 the course of the nutriment tubes. 



Thus far, then, I should be inclined to adopt the 

 nerve-plexus theory. But lastly, we come to another 

 species with a very large bell and a very small polypite. 

 Irritation of margin or radial tubes causes the animal to 

 go into a violent spasm, but irritation of the general 

 muscular layer only causes an ordinary locomotor 

 contraction. On cutting the whole animal into a spiral, 

 and irritating the extreme end of several marginal 

 strips, the entire muscular part of the spiral goes 

 into spasm. On interposing a great number of 

 interdigitating cuts in the course of the spiral, 

 there is no difference in these results. Now the 

 question is, What is the nature of the tissue that 

 conducts impressions from the ganglionic tissue to 

 the muscular, making the latter go into a spasm ? 

 A spasm is as different as possible from an ordinary 

 contraction, and will continue to pass long after the 

 ordinary contractions have been blocked by severity 

 of section. It is scarcely possible to suppose a 

 nerve-plexus here — the tolerance towards section 

 being so great, although it varies in different cases. 

 Besides, suppose this to be a segment of animal cut as 

 represented. On irritating margin at a all the bell 

 goes into a spasm, and it is evident that whatever the 



