96 MEMOIR V. 



(e,) appears to descend considerably lower, and from its 

 acquiring a spherical shape, opake yellowish colour, and its 

 persisting after the death of the animals in many of these 

 Zoophites, is most probably an ovum or ovarium, and quite 

 analagous in situation, with the same organ in the lately 

 discovered compound Ascidise. 



The discovery of the Polyzoa was made in the summer 

 of 1820 ; during the subsequent and following seasons, an 

 exactly similar structure was noticed in the other species 

 above enumerated, and in a new type which perhaps merits 

 to be distinguished as a separate genus, under the title of 

 Pedicellaria,* (PI. II. f. 5, 6, 7,) as the vesicles are single 

 and terminal, each supported by a simple pedicle, origin- 

 ating in a scattered manner, from creeping, slightly branched 

 tubular roots. The Pedicellaria was discovered on the bot- 

 tom of a ship from the United States, mixed with Campa- 

 nulariaAucta, (a new species) and other marine productions. 

 In this type the arms are twelve in number, and the mouth 

 of the animal and tentacula when protruded, incline in a 

 remarkable degree to one side. I for some time thought 

 the Sertularia Syringa might belong to this last type, as it 

 has not been observed to produce any oviferous conceptacles, 

 and although remarkably smaller, bears a considerable re- 

 semblance to Pedicellaria, but as its animal has been since 

 ascertained to be a Hydra, its relation to Campanularia 

 remains undisturbed. 



The Comparative Anatomist will find no difficulty in tra- 

 cing a considerable agreement in structure between Polyzoa 

 and that of the compound Ascidise so admirably developed 

 and so elegantly figured in the Memoirs of Mons. Savigny ; 

 the Polyzoa however are still essentially different, and this 

 difference consists principally in the substitution of external 

 prehensile tentacula, to which the brancliia or respiratory 



* Muller's genus Pedicellaria, harl been erroneously founded on certain 

 productions mixed with the spines in Echini, which are certainly nothing but 

 peculiar organs belonging to tlie animal. 



