*232 Natural History of British Zoophytes. 



polype can scarcely be conceived ; and, perhaps, it is actually the 

 simplest, for the infusory animalcules which had been placed un- 

 derneath them in the scale of organization, are now known to pos- 

 sess a much more complex structure. 



Such is the idea of a polype we obtain from the writings of El- 

 lis, and the description of its general structure given by Lamarck,* 

 after an interval of seventy years, is identically the same. Some 

 few species, classed by the predecessors of the latter among zoo- 

 phytes, had in the meantime been ascertained to be differently con- 

 structed, and furnished with less simplicity, but being in consequence 

 removed into a different category, they were not allowed to disturb 

 the received opinions on polype anatomy. Still more recent disco- 

 veries have shown, however, that these are very erroneous, and that 

 the animals of even our native polypidoms form at least two classes 

 distinguished by a very remarkable dissimilarity of organization. 

 By the one they are allied to the tunicated and acephalous mollus- 

 ca, more especially to the compound families of the former, and hence 

 may be denominated Ascidian polypes ; by the other they form a 

 link of the chain or circle which associates the radiated animals, and, 

 assuming the hydra, for their representative, we shall call them Hy- 

 draform polypes. 



The ascidian polypes never occur in a separate and naked form, 

 but are always placed within the cells of a polypidom of a calcare- 

 ous, membranous, or fibro-gelatinous consistence. The form of the 

 cells in many genera, as Eschara, Flustra and Cellepora, suggests a 

 belief that their tenants, although arranged in a close and determi- 

 nate manner, are each separate from their neighbours and complete 

 in themselves, and this opinion is held by some of our best natura- 

 lists ; but the observations of Professor Grant seem to have proved 

 that the polypes of the Flustra are connected together by a living 



* Anim. s. Vert. ii. 10. Bosc, Vers, ii. 216 — Lamouroux in 1810 and 1812 

 had indeed asserted that the polypes with polypidoms could not, in relation to 

 their structure, he compared with the fresh-water hydra, but that they approxi- 

 mated nearer than was believed to the mollusca, of which they might at some fu- 

 ture time be considered a family. The opinion certainly rested on few and hasty 

 observations, and no anatomical details were given in its support. See his Edit, 

 of Soland. Zoophyt. pref. p. vii. For example, he not only recognizes a relation- 

 ship between Lobularia and Actinia, but he tells us that the polypes of the Flustra?, 

 Cellariae and Sertulariee are similar to those of Lobularia ! Coral. Flex. p. 832. 

 Such loose observations as these are have no influence on the progress of dis- 

 covery. The observations of Savigny were evidently more specific and correct ; 



but I am not aware that the details have been yet published See his Mem. sur 



les Anim. s. Vert. ii. p. 65. 



3 



