JELLY-FISHES 357 



inch or two; then shortened again. Now the little bell 

 resumes its energetic pumping, and shoots round and 

 round in an oblique direction, the summit always going 

 foremost, and the tentacles streaming behind in long trail- 

 ing lines. Now it is again arrested; the bell turns over 

 on one side and remains motionless, and the tentacles, as 

 "fine as silkworms' threads," float loosely in the water, 

 become mutually intertangled, instantly free themselves, 

 pucker and shrivel up, slowly lengthen, and hang motion- 

 less again, or, as the bell allows itself to sink slowly, are 

 thrown into the most elegant curves and arches. 



Though these tentacles look at first like simple threads 

 of extreme tenuity, yet when viewed closely they are seen 

 to be composed of a succession of minute knobs separated 

 by intervals like white beads strung on a thread; the 

 beads being more remote from each other in proportion as 

 the tentacle is lengthened. 



This structure is worthy of a more minute investiga- 

 tion. We will, therefore, confine our little Sarsia in this 

 narrow glass trough, which is sufficiently deep to allow its 

 whole form to be immersed, though somewhat flattened; 

 which is an advantage, as its movements are thereby im- 

 peded. Now, with a power of 300 diameters you see that 

 each of the knobs of the tentacle is a thickening or swell- 

 ing of the common gelatinous flesh, in which are imbedded 

 a score or two of tiny oval vesicles, without any very ob- . 

 vious arrangement; but for the most part so placed that 

 the more pointed end of each is directed toward the cir- 

 cumference of the thickening. The intermediate slender 

 portions of the tentacle the thread on which the beads 

 are strung; is quite destitute of these vesicles. 



These little bodies are called cnidce, and, in the whole 



