272 ZOOPHYTES. 



wander at will by imperceptible progress ; nor are the Virgularia and 

 Pennatula necessarily stationary. 



The Hydra and Actinia, together with the Lucernaria, always enjoy 

 the privilege of selecting their own abode. 



Whether zoophytes actually derive any nourishment through the 

 medium of the root is questionable. 



Notwithstanding the preceding contrasts, it cannot be denied that 

 there is much intimate resemblance between zoophytes and plants. I 

 only wish to express my opinion, that they belong strictly to the animal, 

 not to the vegetable world. Though certain flowers follow the course of 

 the sun, or close as evening comes, we cannot venture to affirm that these 

 demonstrations are the effects of volition. 



4. Stem. — Certain animals comprehended under the order of zoophytes 

 have no proper stem whatever, though rivetted to the same spot ; and the 

 more important parts are elevated above the plane of position. 



Where present, its nature is not always explicit : in form it is cylin- 

 drical, fistulous, plain and smooth, or composed of aggregated tubes, or it 

 is flattened. According to age, size, and substance, it is rigid or flexible. 



The stem of many of the fistulous zoophytes being a simple tube, is 

 occupied by a kind of medullary pith, apparently compact, when vigorous 

 and connected with the living hydras, often seen abundant in decomposi- 

 tion, and copiously discharged from accidental ruptures of the Tubularia 

 indivisa. It is not improbable that the elements of the future embryo 

 have some immediate or remote connection with this medullary substance, 

 being either lodged in, or nurtured by it, or secreted or reposited in its 

 vicinity. The evolution of the young from the pith of the arborescent 

 zoophytes may be distinctly observed. 



The presence of the pith seems indispensable to the life and perma- 

 nence of all the hydraoid zoophytes : with its decay and disappearance ani- 

 mation ceases, and specimens become transparent. 



Whether a similar substance, or any other connecting medium, oc- 

 cupies the stem, or communicating channels with the cells and hydra? of 

 the foliaceous zoophytes, is uncertain. 



