ZOOPHYTES. 231 



sufficient distinction, one class of observers can be hardly expected to sacri- 

 fice the features assumed, as predominant to those which are favoured 

 by another. Hence the perpetual vacillation, which renders it preferable 

 to admit some conventional terra, even though less appropriate, for there 

 cannot be an equal desire for its alteration. 



On this principle, I shall refer to the tenant of the ascidian zoophytes, 

 in much the same signification, as to the hydra of the preceding tribes, 

 and also by the name of hydra. I am not insensible that, by such a lati- 

 tude, I stipulate for a license beyond the strictness which definition would 

 ^llow, but that will prove more than compensated by the advantage of 

 avoiding circumlocution ; nor does it involve the reader in the slightest 

 perplexity. Besides, it obviates that intertexture of words meant to ren- 

 der an intricate compound expressive, though, in truth, they tend to en- 

 feeble and confound each other. The simplicity of definitions from name 

 and character, preserved by such skilful authors as Linnaeus, accustomed 

 to contemplate the grand scale of the animal world ; and of Otho Frede- 

 ric Miiller, viewing it in ample detail, merits modern observance. 



The tenant of the hydraoid zoophytes is comparatively a simple ani- 

 mal ; its internal organization, as that of the hydra, if consisting of various 

 parts, seems very little understood. The tenant of the ascidian zoophyte, 

 where the cellular partition and integuments admit, is seen to be of more 

 complex structure, and by the same means we discover much diversity in 

 their nature. 



While the ascidian hydra is quiescent, the transparence of some zoo- 

 phytes shews it contracted in the cell, doubled on itself, the tentacula 

 compressed together, and the orifice of its habitation closed. As it rises 

 to display its parts, the orificial membrane above is carried upwards, along 

 with the body, and dilates as the body unfolds, like the inverted finger of 

 a glove, turning outwards. Now, it may be observed, that the body of the 

 tenant is attached below, by ligaments regulating its rise and descent ; that 

 the orificial substance of the cell is a continuation of its external intesru- 

 ment, and is carried up from its union with the animal, until the closed 

 pencil of tentacula can display themselves. As the hydra sinks below, 

 the same skin drawn downwards, closes as an operculum over it, when the 



