466 



Mr. G. J. Romanes on the 



[Jan. 11, 



rapid starvation of the smaller segment, owing perhaps to the greater 

 proportional area o£ the nutrient-tube section in it than in the larger 

 segment. It is interesting, however, to note that although a prepotent 

 lithocyst thus situated shows less endurance than the other lithocjsts 

 towards deprivation of nourishment, it shows more endurance towards 

 deprivation of oxygen; for in stale water the prepotent lithocyst will 

 continue active after the others have ceased to discharge, or its action 

 will continue rhythmical after that of the others has become irregular. 



§ 4. Effects of other forms of Mutilation on tJie Wiythm. — Mutilation of 

 a covered-eyed Medusa, in which the series of lithocysts is left intact — such 

 as cutting off the manubrium or portions of the umbrella — causes marked 

 changes in the rate of the rhythm. The first effect of the mutilation is 

 usually to accelerate the rhythm ; but this temporary acceleration gra- 

 dually declines, and eventually the rhythm becomes stationary at a rate 

 slower than that which was manifested by the unmutilated animal. Fur- 

 ther mutilation will now be attended with a repetition of these effects. 

 To show the degree in which these effects occur, I here quote a series of 

 observations. 



An Aurelia manifested per minute a regular and sustained rhythm 



of 26 



Immediately after removal of manubrium rhythm rose to 36 



E-ate then gradually fell for ^ hour, and became stationary at 20 



Circular incision, just including ovaries, caused rhythm to rise to . . 26 



Eate then gradually fell for ^ hour, and became stationary at .... 17 

 Another circular incision, carried midway between the former one 



and the margin, caused rhythm to rise to 24 



Eate again gradually declined, and became stationary at 12 



Another circular incision was then carried round as close to the 

 margin as was compatible with leaving the physiological con- 

 tinuity of all the lithocysts intact : rhythm rose to 14 



Within a few minutes it fell to 6 



Besides producing such marked effects on the rate of the rhythm, muti- 

 lation also frequently produces an effect in impairing the regularity of the 

 rhythm. Tor instance, an Aurelia manifested a regular and sustained 

 rhythm of 36 per minute. Immediately after removal of the manubrium, 

 the rate of the rhythm in successive minutes was as follows : — 40, 39, 37, 

 35, 32, 30, 29, 26, 24, 18, 14 (40 seconds' pause), 16, 15, 14, 15, 16 (40 

 seconds' pause), 22, 20, 19, 15, 16, 17, 14, 13, 13, 15, 16, 17, 18, 14, 12, 

 13, 11, 12, 9, 15, 16, 14, 12, 9, &c., the rhythm now continuing very irre- 

 gular. An hour after the operation the following were the numbers of 

 contractions given in one-minute intervals, the observations being taken 

 at intervals of 10 minutes : — 15, 15, 12, 22, 14, &c. 



These experiments are of interest because tending to show that an 



