ASOIDIA. 139 



abstinence or repletion ; the external form undergoes scarcely any modi- 

 fication from health or disease ; even the lapse of time, that universal 

 consumer, seems hardly to make any impression on the shapeless mass, 

 which is rooted immoveably from the first moment on the same spot to 

 vegetate, live, or die. 



Such is the case, with but few exceptions, during any ordinary or rea- 

 sonable period, that may be occupied in observation. 



Yet, let us recall what is disclosed when this rude object is stripped 

 of its external integuments, from which some of the genus may be with- 

 drawn almost as from a bag. How complex the structure then displayed ; 

 what.a wonderful arrangement of muscular, respiratory, circulating, secre- 

 tive and digestive organs, adapted for discharging the vital functions, 

 all proving the handiwork of the Great Architect, as directed towards a 

 common end. 



To external view, some species of the Ascidia consist of an outer and 

 an inner portion, quite distinct in colour and general appearance ; in 

 others the aspect is wholly homogeneous. Sometimes, in event of a 

 wide rent, or great rupture of the outer coating, the red internal substance 

 escaping, leaves the rest as clear as crystal behind. 



The Ascidia, I should repeat, does not properly belong to that exten- 

 sive tribe with which we have been engaged — the zoophytes ; for those 

 brought under review only participate of its nature. But, by assuming a 

 discretionary latitude, it receives a few illustrations here, principally as 

 another introduction to certain natural products of compound formation, 

 wherein its properties hold an important place. 



Besides these, their nature distinguishes many of the testaceous genera, 

 of which I shall say nothing at present, unless that it may be seen how 

 extensively the genus is distributed, and under how great a variety of 

 aspect and combination. 



Almost the whole Ascidise with which I am acquainted, are perma- 

 nently affixed to some foreign substance. I have not seen above two ex- 

 ceptions ; and the whole Ascidise proper are inhabitants of the sea. 



The external aspect of this animal is much diversified. Some, dark 

 and opaque, clumsy, or inactive, resemble the root of a vegetable ; some 



