SECTION OF COVERED-EYED MEDUSZ. 93 
| Time occupied in passage of 
Temperature of water. contractile waves. 
26° 4. seconds. 
a2 3 seconds. 
42° 22 seconds. 
65° 2 seconds. 
75° 12 seconds. 
85° Blocked. 
Or, adopting again thegraphic methodof statement, 
these variations may be represented as follows :— 
= See eneea 7 — 
A 
85 = fee Wave blocked 
One second ve | 
Fig. 16. 
Submitting a contractile strip to slight strains has 
also the effect of retarding the rate of the waves 
while they pass through the portions of the strip 
which have been submitted to strain. The method 
of straining which I adopted was to pass my finger 
below the strip, and then, by raising my hand, to 
bring a portion of the strip slightly above the level 
of the water. The irritable or contractile surface 
was kept uppermost, and therefore suffered a gentle 
strain; for the weight of the tissue on either side 
of the finger made the upper surface somewhat 
convex. By passing the finger all the way along 
