FILIFEROUS CAPSULES. 79 



derived, may be traced upwards along the corresponding septum as far 

 as a little above the inferior termination of the alimentary cavity, and 

 then running along the external wall of the stomach as far as the py- 

 loric opening. The structure of the terminal portion as well as that of 

 the convoluted filament is tubular, and their office apparently important 

 in the economy of the animal : M. de Blainville regards them, with 

 some probability, as representing the biliary system. 



(174.) The Abbe Dicquemare relates several curious experiments 

 on the multiplication of these animals by mechanical division. When 

 transversely divided, the upper portion still stretched out its tentacles 

 in search of food, which, on being swallowed, sometimes passed through 

 its mutilated body, but was occasionally retained and digested. In 

 about two months, tentacles grew from the cut extremity of the other 

 portion, and this soon afterwards began to seize prey. By similar sections 

 he even succeeded in making an animal with a mouth at each end. 



(175.) After the account .above given of the general structure of 

 the Actinia, the mechanism whereby the tentacula are expanded and 

 withdrawn will be easily understood : these do not, like the horns of a 

 snail, become inverted and rolled up within the body, but owe their 

 different states of extension entirely to the forcible injection of water 

 into their interior. We have seen already that the cavity of each 

 tubular arm communicates freely with the space intervening between 

 the stomach and the external integument a space which, at the will 

 of the animal, is filled with sea-water drawn through the orifices placed 

 at the extremity of each arm : when these minute orifices are closed, 

 and the body of the creature contracted, the water, being violently 

 forced into the tentacula, distends and erects them, as when watching 

 for prey ; and, on the other hand, when emptied of the fluid thus in- 

 jected, they shrink and collapse. This circumstance, so easily seen in 

 the Actiniae, will likewise enable us to account for similar phenomena 

 observable in other polyps, the internal economy of which is by no 

 means so conspicuous. 



(176.) On cutting off a portion of one of the arms of an Actinia and 

 subjecting it to pressure, it is seen to have, imbedded in the substance 

 of its gelatinous parietes, an immense number of minute organs, now 

 universally known by the name of filiferous capsules. These remark- 

 able structures, which are found to exist very extensively throughout 

 the entire group of polypoid organisms, consist of minute sacculi, 

 wherein may be perceived a slender and highly elastic filament coiled 

 up spirally, but which, on compression, suddenly shoots forth from one 

 extremity of the capsule to a length that is perfectly surprising. It is 

 upon the presence of these filiferous capsules that the adhesive power 

 of the tentacula is supposed to depend ; and from the rapidity wherewith 

 prey, when seized, is destroyed by their grasp, it is probable that a 

 poisonous fluid is emitted along with the thread, to the virulence of 



