ZOOPHYTES. 229 



rather from presuming what the internal parts ought to be, at least in cer- 

 tain respects, than from truly discovering what they are. The resemblance 

 presented is only a modification, of which the skilfril microscopician may 

 convince himself ; yet we cannot deny that it may approach the fact. 



For satisfactory elucidation of the structure and history of some 

 Ascidian zoophytes, let me refer the reader to the very copious memoir 

 of an intelligent author, Dr Farre, in the Philosophical Transactions for 

 1837, together with the useful abstract and illustrations by Dr Johnston, 

 in his general treatise on British Zoophytes. In the former, the anatomy 

 of several species is distinctly explained ; and a few notices relative to the 

 propagation of the respective genera, all accompanied by numerous figures. 



Perhaps the subject of the ascidian zoophytes should be introduced 

 with some more special commentary on the form and the habits of the 

 Ascidia itself. But independently of their combination with a foreign 

 substance, which I have not seen in any of the Ascidia proper of Scot- 

 land, the tenants of that substance are, not real Ascidiae, being only parti- 

 cipants in certain analogies, nor these of a very intimate kind. 



No greater apparent difference can separate two animals of opposite 

 genera than the external character of the Ascidia proper and the ascidian 

 zoophyte. The former resembles a mass of mere inanimate matter, com- 

 monly rooted to the same spot or substance, which it is incapable of quit- 

 ting. It scarcely betrays the rudest indication of any propensities or 

 instincts. All its changes, alterations, and actions are confined to an al- 

 most insensible enlargement of the body from the absorption of water, 

 slight dilatations of its orifices for the reception and discharge of muddy 

 matter. The rigidity of the body of the majority of the Ascidiae restrains 

 either its distention or contraction. Their whole sensations seem more ob- 

 tuse to external impressions than those of most living creatures. Hence are 

 their habits and configuration so little calculated to invite notice ; nor 

 until stripped of the coriaceous exterior covering, is the curious internal 

 structure laid open to the beholder. Hence also is almost all that has 

 been said of the ascidian tribe confined to anatomical formation. 



As I shall probably resume a few general observations on the Ascidia 

 in a subsequent section, the reader may be here referred to the ample in- 



