140 ZOOPHYTES. 



structure of these parts, the articulations and whirls, are obscured, which 

 has induced naturalists finding them, exposed with the death of the pro- 

 duct, and still permanent when it was preserved, to seize their characters 

 for the basis of arrangement. 



But the consistence of the body of the creatures belonging to the 

 Sertulariae is apparently not remote from that of the hydra proper, al- 

 lowing some difference between those of hydraoid and ascidian formation. 

 Although these tenants of the zoophytes be liable to perish from natural 

 or accidental causes, their parts are by no means simply gelatinous, void 

 of coherence and tenacity. Many of the ascidian are bound by ligaments 

 to the interior of the cell, which aid their rise and descent ; and in some, 

 as the Alcyonidium parasiticum, the connection being ruptured, hundreds 

 drop entire from their cells when the salubrity of the surrounding element 

 is vitiated. 



The nature of the asteroid zoophytes is different. The body of the 

 hydra, rather fleshy, there forms an integral portion of the common sub- 

 stance belonging to the whole, from which it cannot separate by decay. 



From this diversity of consistence, whereon diversity of structure is 

 concomitant, these minute beings are endowed with a very different share 

 of strength and tenacity of life. Those denominated helianthoids, as the 

 Actinia, are the strongest of any comprehended among the race of zoo- 

 phytes. They are void of a place of shelter ; but some of the Sertularian 

 hydrse can scarcely endure speedy transference to a fresher element. Re- 

 moval from their native abode is generally fatal after the shortest season. 

 Zoologists should thence value the correct delineation of perfect speci- 

 mens as an accession to their knowledge of the animated world. 



The life of the specimen is dependent on the subsistence of the pith ; 

 the life of the hydra on its connection with the body, but not of the con- 

 tinuity of the pith in the stem or in the other tubular parts. The life of 

 each of a thousand individuals, though all sustained by diverging parts, 

 supported on a single common stem, as rising from the root, is independent 

 of that which animates all the rest. Though all may have been generated 

 from elements reposited in the pith, whence their origin has been derived, 

 the death of no one individual seems to affect its neighbour. While the 



