vii AN EXPERIMENT ON AURELIA 345 



I must here refer to a particular experiment which bears 

 upon this subject. 1 It must be explained that in Aurelia 

 aurita, on which the experiment was made, there is an anus 

 between every two marginal bodies. 



On 29th August, at 12 noon, of two specimens of Aurelia 

 18 cm. in diameter, I cut away from one the marginal 

 bodies, from the other the parts around the anal openings. 

 The first remained after the operation entirely motionless, 

 the second contracted as usual. In the former, twitchings 

 occurred only when I pricked it with a needle slight 

 imperfect contractions. 



Second day. 30th August, 11 A.M. The animal (0) 

 deprived of its marginal bodies lies flat, extended, and motion- 

 less, the remaining parts of the margin somewhat turned 

 upwards. Even when pricked with a needle it reacts extremely 

 feebly. The other specimen (M) still contracts actively. The 

 separated pieces of contract vigorously, as they did yester- 

 day immediately after their removal ; the separated portions 

 of M have, on the contrary, lost their fresh appearance, they 

 are no longer elastic, but flabby and thin they seem to be 

 dead, for not even the tentacles on them react to stimulation. 



Third day. 31st August. M contracts most vigorously (in 

 the same water) at least ten times per minute, but generally 

 much oftener. On still not a single contraction is to be 

 perceived. 



Fourth day. 1st September, 12 noon. M contracts (in the 

 same water) vigorously. makes at intervals of 2|, 1|, 1| 

 minutes slight contractions, but only with two particular 

 anal lappets out of the eight, and these two contract 

 simultaneously. "When the animal is pricked in the centre 

 with a needle, the same two lappets which exhibit spon- 

 taneous movements contract strongly, and some of the others 



1 It is described as Experiment D at p. 81, et seq., of the Medusae. Cf. fig. 5 

 below. The dotted lines in the figure terminate on the margin at the anal apertures. 



