TUNICATA. 3 



by gemmation. In these latter characters, so very im-- 

 portant in a physiological point of view, they ajiproach 

 closely polypes ; and if we compare the general conforma- 

 tion of their bodies with that of the Escharee, Vesiculariae, 

 Halodactyles, Pedicellaria?, and other zoophytes, for which 

 I have proposed the designation of ' Polypes Tuniciers,*' 

 one cannot but perceive other analogies not less striking — 

 the mode of aggregation through which most of them are 

 united in societies, and their phytoid aspect. To harmo- 

 nise the zoological classification with our anatomical know- 

 ledge, it seems to me convenient no longer to confound, with 

 Cuvier, the Tunicata with the JSIollusca, but to follow 

 Lamarck, and constitute for them a special division inter- 

 mediate between the bivalve Mollusca and the polypes/' 

 The force of this proposal, however, depends mainly upon 

 the view to be taken of the classification of the zoophytes 

 themselves. And, in the present state of our knowledge, a 

 blank would occur in such a series of works on the Natural 

 History of Britain as that of which this forms a part, unless 

 some account of the Ascidians were therein given. 



We shall commence, then, our history with a short 

 notice of the Mollusca of the order Tunicata. Our main 

 object m this work is to give a full account of the Testa- 

 ceous Mollusks of the British Islands, but it is necessar}-, 

 in order to connect them in zoological order, to notice the 

 shell-less tribes. To treat the latter fully, or on nearly the 

 same scale with the shelled species, would be to extend 

 these volumes to an encyclopedic length ; nor is it necessary, 

 for the beautiful monograph of the " Nudibranchiate Mol- 

 lusca," by our friends Mr. Alder and Mr. Hancock, ex- 

 hausts one portion of the subject, whilst for the other, 

 equal in extent, that of the Tunicated Mollusks of the 

 British seas, which we are now about to outline, though 

 great masses of materials have been collected by the com- 

 bined labours of many naturalists, and are now safely in 

 chargeof Professor Goodsir, by whom, we trust, they will be- 

 fore long be worthily examined and made known, to work 

 them will be a labour of several years, and many more ob- 



