1 6 PULSATION OF JELLYFISHES. 



VITALITY, ETC. 



The fluids of the central stomach of Cassiopea are practically neu- 

 tral to litmus test, whereas the sea- water at Tortugas is decidedly alka- 

 line. For example, litmus paper tinged pink by HC1 is changed to 

 blue in the sea- water in from 9 to 12 minutes, whereas a portion of 

 the same litmus paper thrust into the central stomach cavity of 

 Cassiopea will not become blue until it has remained in the stomach 

 for 6 to 9 hours. The whole surface and all of the tissues of the 

 Medusa are almost neutral and much less alkaline than is the sea -water. 

 The stomach cavity may be filled with sea-water charged with CO 2 

 or we may place crystals of K 2 SO 4 within it, and } 7 et little or no effect 

 will be produced upon the movements of the Medusa, although, as we 

 shall see, these substances produce a profound effect if applied to the 

 sub-umbrella surface. Remarkably little CO 2 is given off by the 

 Medusae in metabolism. A large Medusa was confined for 12 hours 

 in a small quantity of sea-water tinged pink by rosolic acid, and the 

 decoloration of the fluid was barely perceptible. 



Cassiopea pulsates regularly and at its usual daylight rate through- 

 out the night, and even red light has no apparent effect upon its rate 

 of movement. If long confined in absolute darkness, however, the 

 rate of pulsation becomes slower, and the plant cells within the tissues 

 of the Medusa become shriveled and greatly reduced in number, so 

 that the Medusa becomes pale blue in color and translucent. Only 

 the filaments of the mouth-arms retain their greenish color. (PI. n, 

 fig. B.) The whole color of the Medusa becomes lighter and more 

 uniform than the normal, as will be seen upon comparing figures A 

 and B of plate n. Two Medusae of Cassiopea xamachana were main- 

 tained in absolute darkness and without food for one month. When 

 first placed in the dark their diameters were 82 and 42 mm., and their 

 rates of pulsation 40 to 50 and 51 to 54 per minute, respectively. At 

 the end of one month the large Medusa had shrunken so as to be but 

 58 mm. and the small one 25 mm. in diameter, and their rates of pul- 

 sation 23 and 17 per minute, respectively. On their being removed 

 to the diffused daylight of the laboratory, the color remained un- 

 changed for three weeks, but the diameters of the Medusae continued 

 to decrease; finally, however, the plant cells in the mid-region of the 

 sub-umbrella and ex-umbrella became dark brown and densely crowded, 

 so that these parts of the Medusae were dull brown in color. After 

 being in the light for one month the large Medusa was only 29 mm. 

 in diameter, and its rate of pulsation was less than i per minute. 



On the other hand, when the Medusa is maintained without food in 

 the light it becomes dark brown in color (pi. 11, fig. c), as will be 

 seen upon comparing its photograph with that of a normally colored 



