POLYPI. 81 



and whether the Trichina spiralis may not belong to the same 

 category. But how these embryos (if they be embryos) are diffused 

 through the intermuscular cellular tissue, can only be known after 

 long and laborious investigations : and nothing is more true than 

 that a particular enquiry will be required for each particular species. 



LECTURE YII. 



POLYPI. 



The two great divisions of the sub-kingdom Zoophyta, — viz. the 

 Infusoria and Entozoa, which have hitherto engaged our attention, 

 approximate to the vermiform type ; and each ascends by rapid steps 

 to the confines of the articulate sub-kingdom. The remaining classes 

 of the Zoophyta are constructed on the radiated type, and some 

 of them, as the Bryozoa and Acalephce^ conduct to the molluscous 

 series. 



To-day I have to request your patient attention to the history of a 

 race of animalcules as widely diffused, almost as numerous, and some 

 of them hardly less minute than the Infusoria^ with which we com- 

 menced the survey of the vermiform zoophytes. Our present subjects 

 form at least three classes of radiated zoophytes, which have been 

 grouped together under the common name of Polypi, on account of 

 their external resemblance to the many-armed cuttle-fishes, which 

 were so denominated by the ancient Greek naturalists. But the 

 knowledge of the organised beings now called Polypi, as members 

 of the Animal Kingdom, is of comparatively recent introduction : 

 it cannot be dated further back than the time of Imperato* and 

 Peyssonel.f Amongst those naturalists who have subsequently con- 

 tributed to improve and extend the history of the Polypes, our 

 countryman Ellis will always take a high rank. 



A polype generally presents a cylindrical or ov 1 body, with an 

 aperture at one of its extremities, which is surrounded by a coronet 

 of long tentacula. In most of the class this aperture leads to a simple 

 digestive cavity, consisting of a stomach without intestine : in the 

 higher organised species, the digestive sac is prolonged into an intes- 



* Historia Naturale, fol. 1599. 



t Traite du Corail, Phil. Trans. 1756; communicated to the French Academy, 

 1727. 



