88 ZOOPHYTES. 



portion over the origin of which they do not evidently possess any secret- 

 ing influence or mechanical controul. 



The family is small, consisting of but a few genera or species ; and 

 all are inhabitants of the fresh-waters of this country. 



We shall have a future opportunity of offering a few observations on 

 a marine animal, indeed, of infinitely larger size, with the higher external 

 organs of somewhat corresponding office and conformation. But there is a 

 material difference between the two, for the latter, inhabiting the sea, 

 fabricates an artificial dwelling for its own protection, by a most peculiar 

 and interesting mechanical process, not to be equalled by human skill. 

 It cannot be incorporated with the subject now under discussion, though 

 many analogical features may be displayed by both. 



The polypus of the fresh-waters or common hydra, and the Ascidia 

 proper of the sea, occur as simple animals unconnected with any polyparium, 

 sheath, or receptacle for their retreat. The same remark will apply to 

 the Hydra or Corgua squamata, and, as we have seen, to the Pedicellina, 

 besides some others ; nor is there such shelter to be obtained for the 

 Cori/iia glandulosa, whereof so very little seems to be known. But, in as far 

 as I am aware, a polyparium is uniformly present in combination with the 

 lunate ascidian zoophytes ; and sometimes it is of large dimensions. 



It should be observed, however, that although the polyparium of any 

 of the zoophytes may enlarge to unwieldy bulk, this ensues without in- 

 fluencing that of the inhabitants. Their size seems to remain always the 

 same. It seems always alike diminutive, at least no sensible alteration 

 is discovered, though I will not venture to deny, that some enlargement 

 of the present, or of a subsequent generation, may follow. 



In certain respects a correspondence may be found between the poly- 

 parium of the lunate ascidian hydra?, to several of those already described, 

 and especially to that of the Flustra hispida ; notwithstanding, they are 

 widely apart in points alike characteristic, if not more so. 



The lunate hydra? of Scotland falling within the sphere of my obser- 

 vation, are of three distinct genera — each appearing under a very different 

 aspect. All are marked by the strongest features, and are deeply interest- 

 ing to the physiologist. 



