32 Papers from the Marine Biological Laboratory at Tortugas. 



The influence of temperature on the sense-organs apart from other 

 tissues can be studied by the method indicated in fig. 2. The sense- 

 organs are in A and the sea-water is 

 slowly warmed. Cessation of contrac- 

 tion in B indicates that the stimuli 

 are no longer given out by the sense- 

 organs. 



The thermometer used had been 



p IG 2 standardized and was graduated to 



0.1 C. The rate of change of tem- 

 perature was kept as constant as possible, 1.0 in 2 minutes. 



LOWERING THE TEMPERATURE. 



Cooling of the sea-water containing normal medusae produces at 

 first a rapid pulsation, but the rate per minute gradually decreases at 

 lower temperatures. At about 18 Cassiopea begins to turn inside out, 

 the subumbrella surface becoming convex and the exumbrella concave. 

 This relaxation, as it may be called, is also characteristic of diseased 

 (by parasites) and dying (in stale or constantly agitated sea -water) 

 jelly-fish. The fact that it begins at 18 to 19 shows how sensitive the 

 animal is to a decrease in temperature. The summer temperature of 

 the sea-water at Woods Hole is about 18, whereas on the California 

 coast Loeb 1 reports the temperature of the water to be about 10 and 

 the eggs of Strongylocentrotus fail to develop above 23. 



Using the methods illustrated in figs, i and 2, it was found that the 

 functioning of three different tissues ceases at the following temperatures: 

 sense-organs (pulsation), 14 C. ; muscles (contraction), 9.5 to 10.6; 

 nerves (conduction), 8.8 to 9.5. 



If cooled to 9.5 and immediately returned to sea-water at 29 

 there is complete recovery, but there is no recovery if cooled to 7 to 8 C. 

 The tissues disintegrate on warming, whether warmed suddenly or 

 slowly. This fact is especially interesting, as, with the exception of 

 warm-blooded animals, few forms are killed by exposure to low tem- 

 peratures, but above the point at which ice crystals form. 2 Irreversible 

 changes do not take place in all jelly-fish, however, as Romanes 3 reports 

 freezing Aurelia aurita solid in a block of ice, yet there was complete 

 recovery on thawing. 



RAISING THE TEMPERATURE. 



A sudden rise of temperature brings about a sudden increased pulsa- 

 tion of the normal medusa, but this increase is not so marked as with 

 lowering. Relaxation begins about 36. The tissues cease to function 

 at about the following temperatures: muscles, 4 39.5; sense-organs, 

 42.6; nerves, 44.0. 



1 Loeb, J., Arch. f. d. ges. Physiol., 124, p. 417, 1908. 



2 See Loeb's discussion in Dynamics of Living Matter, p. no. 



3 Romanes, J. J., Jelly-fish, Star-fish, and Sea-urchins, International Scien- 

 tific Series, New York, 1885, vol. XLIX, p. 167. 



4 The circular muscles cease perhaps 0.5 before the radial muscles, but this 

 difference is not always constant. 



