ME. Gr. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSAE. 
677 
quiescence, which were broken by occasional single contractions and occasional bouts of 
partly rhythmical swimming-motions. These bouts could at any time be pretty certainly 
evoked by a stimulus, and the rate of their imperfect rhythm was about 10 per minute.” 
§ 6. Effects of Temperature on Rhythm, {a). — The effects of temperature on the 
rhythm of Medusae are very decided. For instance, a specimen of Sarsia which in suc- 
cessive minutes gave the following numbers of pulsations — 16, 26, 0, 0, 26, gave 60 pul- 
sations during the next minute, while a spirit-lamp was held under the water in which 
the Medusa was swimming. If hot water be added to that in which Sarsia are contained 
until the whole is about milk-warm, their swimming-motions become frantic. If the 
same experiment be performed after the margins of the Scirsia have been removed, 
the paralyzed bells remain quite passive, while the severed margins exhibit the frantic 
motions just alluded to. 
In the case of Aurelia aurita the characteristic effects of temperature on rhythm may 
be better studied than in that of Sarsia, from the fact that the natural motions are more 
rhythmical and sustained in the former than in the latter genus. I have therefore, in 
this connexion, made more observations on Aurelia than on Sarsia. The following, 
quoted from my notes, may be taken at a typical experiment : — 
“ A small and active specimen of Aurelia contracted with the greatest regularity 33 
times per minute in water kept at 34°; but on transference to water kept at 49°, the 
contractions always became irregular, in respect ( a ) of not having a perfectly constant 
rhythm, and (h) of exhibiting frequent pauses, which was never the case in colder water. 
The rate of rhythm in the warmer water varied from 37 to 49 ; and, as in these obser- 
vations no allowance was made for the occurrence of the pauses, the actual rate of 
rhythm during the swimming-motions was about 60 per minute. The following are 
some sample observations in the case of this specimen : — 
Eate of Ehythm in successive Minutes. 
Temperature of water (Fahr.). 
Number of pulsations. 
Seconds of rest. 
49 
41 
5 
„ 
49 
4 
Transferred to 34 
33 
0 
„ 
33 
0 
„ ,, 
33 
0 
„ „ .... 
33 
0 
Transferred to 49 
45 
4 
„ „ 
39 
10 
„ 
37 
15 
Transferred to 34 
20 
. 0 
„ „ 
30 
0 
„ „ 
33 
o 
„ „ , 
33 
0 
„ ,, 
33 
0 
1 ■ 1 
33 
o 
5 c 2 
