1G2 F. A. BEDWELL ON THE URTICATING THREADS OF 



which found out the favourite haunt of the hermit crab in an 

 aquarium, and waited its opportunity to slide off the rockwork on 

 to his shell, are some of the instances of its extraordinary habits and 

 gifts. But I became acquainted in 1868, at Swanage, with an in- 

 cident connected with this crab and actinia, which may be of interest. 

 I noticed that when fresh specimens were put into an aquarium the 

 pair soon parted company, and the following morning the hermit crab 

 would usually be found to be dead, with a wound in its side. On look- 

 ing round for the enemy that had assailed him I found that most of 

 the shells actually had a third inmate, in the form of a large worm 

 (see fig. 8), which, with a most ferocious pair of jaws concealed 

 in its body, had killed the crab. As to which of the triumvirate 

 (if either) destroyed the whelk in the first instance, I do not pretend to 

 say, but I strongly suspect one of the three did it ; perhaps not the 

 actinia, as I have seen parasitica very contentedly riding on 

 a shell with the whelk itself inside ; but, at any rate, here are 

 three animals living in or on a house they never made, the 

 crab dragging for all and digging for all, and the actinia, by the help 

 of its fishing lines, picking up from the diggings of the crab the 

 annelids, amoeba, etc., that he disturbs, the worm (fig. 8) living on 

 the leavings of the actinia, and then winding up the scene by eating 

 into the crab, because he does not move fast enough, or because food 

 gets scarce in a contracted aquarium ! 



I agree with Mr. Gosse that the threads are weapons of offence 

 and defence, as the Actinia ejects them on irritation ; but there is 

 this curious circumstance about them, that at last the animal gets 

 accustomed to being touched, and will not eject them. And after a 

 very little time, when I wanted to obtain a piece of thread for ex- 

 amination, I had to insert a crochet needle gently into the oval 

 aperture and fish up one for myself. At first the animal resented 

 this intrusion, and closed its disc, but it soon became accustomed to 

 that also, and latterly never stirred when I introduced the needle. 

 Undoubtedly the threads must assist digestion, even when within the 

 body, by destroying and disintegrating the small living objects which 

 are brought into the inner chambers by the constant currents to 

 be seen passing in and out of the two little gristly-looking 

 angles or channels (gonidia, Gosse), situate one at one corner of the 

 oval aperture and the other at the other, and which are usually 

 kept open, however closely the stomach walls may have come together 

 and closed up the oval aperture. 



