22-4 SINGULAR USE OF ITS DISK. 



disk, of thrice the diameter of the body ; its substance 

 was gelatinous, full of oblong granules arranged con- 

 centrically. (See fig. 4.) I neither saw this disk 

 evolved nor retracted ; but after some time, on looking 

 at it, the same phenomenon was repeated. In order 

 to obtain a better sight of it, but without a suspicion 

 of what I was about to effect, I slightly turned the 

 tube of the box, carrying with it the alga to which the 

 polype was attached, my eye upon it attentively 

 observing all the time. The base of the polype moved 

 away from its position, but the broad disk was im- 

 moveable ; I continued to turn the upper glass, until 

 at length the body was dragged out so as to be con- 

 siderably attenuated ; still the disk maintained its 

 hold of the lower glass, with no other change than 

 that of being elongated in the direction in which it 

 was dragged. At length it slowly gave way, and 

 resumed its original shape by gradual and almost 

 imperceptible diminution of the circumference. 



The oval grains of the tentacle-heads appear to be 

 packed in a gelatinous substance which fills their 

 interstices, and envelopes the whole, which is then (I 

 think) inclosed in a thin calcareous shell, for it breaks 

 with a loudish crepitation under pressure. It is pos- 

 sible however, that this crackling may have indicated 

 the crushing of the grains themselves.* They often 

 get loose from the heads without pressure, and then 



* At this time I was not familiar with the filiferous capsules of the 

 Helianthoid Zoophytes. I will not cancel my recorded impressions of 

 the actual observation ; but I now think that it is likely the granules 

 were filiferous capsules, the crepitation that which marks the emission 

 of the thread, and the "film of jelly," possibly the filament itself. 



