140 ZOOPHYTES. 



are not unlike small or large red currants. Many may be compared to a 

 diminutive sackfull of grain or other commodities, and a few are of a beau- 

 tiful green, glassy, translucent colour. I speak only of those of more com- 

 mon occurrence, such as are not difficult to be procured. 



If any of those in adhesion be detached they seldom fix again. Though 

 undergoing no sensible alteration, and adhering firmly to the substance 

 whereon it is implanted, the two orifices of the body of the Ascidia are 

 often contracted and dilated alternately, the higher being appropriated for 

 the absorption of nutritious matter, and the lower, the termination of the 

 intestinal canal. 



The food of the animal seems to consist in what may be eliminated 

 from muddy solutions. Quantities of mud suspended in water are evi- 

 dently absorbed and long retained ; they visibly fill the intestinal cavities 

 of those species whose transparence exposes the interior. If the clearest 

 sea- water be rendered turbid, it is speedily purified by the secerning ope- 

 ration of internal organs, serving to select the nutrition, while the residue 

 is rejected, to be discharged in rolls or cylinders. 



Most Ascidiae are sufficiently hardy to survive long in captivity with 

 due precaution for frequent renewal of their element, and to preserve 

 them from pressure. Though numerous colonies may be crowded together, 

 and certainly suffer pressure among themselves with impunity in their na- 

 tural abodes, all artificial pressure, even where slight, seems always fatal. 



Probably this creature attains very great age. Specimens bear un- 

 doubted evidence of the fact. The surface serves as a fertile soil for the 

 o-erminating fuci. or the implantation of zoophytes. Several of the cirri- 

 pedes and testacea find a permanent habitation there ; and may be occa- 

 sionally found entirely overgrown and incorporated with the flesh. 



Naturalists have hitherto paid very little attention to the living As- 

 cidia. Indeed, we must own, that an animal displaying such indefinite 

 habits, those scarcely to be distinguished, is not likely to attract notice. 

 A copious and excellent treatise, chiefly anatomical, was published above 

 thirty years ago, on the simple and compound Ascidia-, by M. Savigny, a 

 learned French physician, illustrated by numerous interesting plates. A 

 treatise by M. Milne Edwards on the subject in detail, was published in 



