IV. Z O O P H Y T A ASCIDIOIDA. 
FAMILY IX. VESICULARIADiE. 
Since we profess to be guided, in the classification of zoophytes, by simi- 
larity in the structure of the polypes considered independently of their poly_ 
pidoms, the Vesiculariadse, notwithstanding their apparent dissimilarity, must be 
associated in the same order with Alcyonidium and Flustra. They have been 
hitherto united with the Sertulariadae, and previous to our knowledge of their 
polypes, this seemed a very natural union, for the polypidoms of both are slen- 
der and plant-like, horny, fistular and flexible, and furnished with somewhat si- 
milar cells on their branches. But the differences between them even in out- 
ward aspect are not inconsiderable, and although it may be difficult to point out 
these by any description, they are nevertheless not the less obvious to one fa- 
miliar with the objects. The polypidoms of the Vesiculariadse are more flexible 
and of a thinner texture, less arboreal and more confervoid, not so regularly 
jointed, nor ramified in the same determinate and fixed manner. They are all 
marine productions, generally not more than an inch or two high, and are found 
attached only to sea-weeds or other corallines. 
For a knowledge of the animated tenants of these structures we are indebted 
to Cavolirii, the Rev. Dr Fleming, J. V. Thompson, Esq. and more particularly 
to Dr Farre, of whose researches a summary has been given in the preliminary 
observations. The following is his description of the cells in the present fa- 
mily : 
“ The transparent horny cell which closely embraces the body of the animal 
is nearly unyielding in its lower two-thirds, but terminates above by a flexible 
portion, which serves to protect the upper part of the body when the whole is 
