146 Mr. G. J. Romanes on the [Dec. 16, 



tion, is of a very marked character ; for the spasmodic movements of the 

 nectocalyx are as easily and as certainly excited by irritating any part of 

 the severed strip as they are by irritating the substance of the nectocalyx 

 itself. 



From this description it will readily be seen that a Medusa, when thus 

 operated upon, supplies all the conditions required for conducting experi- 

 ments in electrotonus : the animal in this form is, for all practical pur- 

 poses, a nerve-muscle preparation. Accordingly I have spent a great 

 deal of labour over this part of my subject, but with no very satisfactory 

 results. In the case of Staurophora lacinlata, however, I have sometimes 

 obtained decided indications of kathelectrotonus, but never any of anelec- 

 trotonus. I cannot yet speak decidedly with respect to Pfliiger's law. 



(d). oc. The excitable tissues'of Medusae, although somewhat capricious 

 in the comparative sensitiveness they show to make and break of the 

 current, upon the whole conform to the rules which are followed by the 

 excitable tissues of other animals. 



(j. Different species of Medusas manifest differences in the degree of 

 their sensitiveness to electrical stimulation. In all cases, however, the 

 degree of sensitiveness is wonderfully high. 



y. When the constant current is passing in a portion of a strip of a 

 severed margin, the nectocalyx sometimes manifests uneasy motions 

 during the time the current is passing ; this, however, is perhaps due to 

 variations in the intensity of the current. 



I. When the intrapolar portion of the severed margin of S. laciniata 

 happens to be spontaneously contracting prior to the passage of the con- 

 stant current, the moment this current is thrown in such spontaneous 

 contractions usually cease, and are seldom resumed until the current 

 is again broken, when they are almost sure to recommence. This 

 inhibitory effect may be produced a great number of times in suc- 

 cession. 



e. Exhaustion of the excitable tissues may be easily shown by the 

 ordinary methods. Exhausted tissue is much less sensitive to stimula- 

 tion than is fresh tissue, and, so far as the eye can judge, the contrac- 

 tions are slower with the period of latent stimulation prolonged. 



£. Tetanus produced by Earadaic electricity is not of the nature of an 

 apparently single prolonged contraction (except, of course, such of the 

 naked-eyed Medusae as respond to all kinds of stimuli in this way), but 

 that of a number of contractions rapidly succeeding one another. There 

 is hence no appearance of summation. 



-q. When the swimming-bell of Sarsia has had its margin removed, and 

 so (as proved by hundreds of experiments) has been entirely deprived of 

 its locomotor centres, nevertheless, in response to electrical stimulation, 

 instead of giving a single contraction to make or break, it may begin a 

 highly peculiar motion of a flurried, shivering character, which lasts 

 without intermission for periods varying from a few seconds to half an 



