POLYZOA. 463 



of organs connected with the higher senses, and unable to change their 

 position, are content to cast out at intervals their ciliated arms, which 

 form a net of Nature's own contrivance, and thus entrap such passing 

 prey as suits their appetite. Others, equally incapable of locomotion, 

 but furnished with arms of different construction (BRACHIOPODA), catch 

 their food by similar efforts. The TUNICATA, enclosed in coriaceous 

 bags, are firmly rooted to the rocks ; or, aggregated into singular com- 

 pound masses, float at the mercy of the waves. The CONCHIFEEA inhabit 

 bivalve shells ; while the GASTEROPOD orders, likewise defended in most 

 cases by a shelly covering, creep upon a broad and fleshy ventral disk, 

 and, thus endowed with a locomotive apparatus, exhibit senses of pro- 

 portionate perfection. The PTEKOPODA swim in myriads through the 

 sea, supported on two fleshy fins ; while the CEPHALOPOD MOLLTTSCA, the 

 most active and highly organized of this large and important division of 

 animated nature, furnished with both eyes "and ears, and armed with 

 formidable means of destroying prey, become tyrants of the deep, and 

 gradually conduct us to the most exalted type of animal existence. 



(1194.) These different sections, which constitute, in fact, so many 

 distinct classes into which the HETEROGANGLIATA have been divided by 

 zoologists, we shall now proceed to examine seriatim ; beginning, as 

 heretofore, with the most imperfectly organized, and gradually tracing 

 the development of superior attributes and more exalted faculties as the 

 nervous centres attain greater magnitude and concentration. 



CHAPTER XVIII. 



POLYZOA (Thompson). 

 BRYOZOA* (Ehrenberg). CILIOBRACHIATE POLYPI (Farre). 



(1195.) IT is only within the last few years that microscopical 

 researches have revealed to naturalists the real structure of a series of 

 animals originally confounded with the simpler polyps, with which, as 

 far as external form is concerned, they are indeed intimately related. 

 The observations of Milne -Edwards f, Audouin, Ehrenberg $, and 

 Thompson gradually led the way to more correct and precise ideas 

 concerning the more highly- organized genera ; while Dr. Arthur Farre || 

 and Yan Beneden, by a series of investigations followed up with exem- 

 plary industry and perseverance, seem to have completed our knowledge 



* jSpvov, sea-moss ; o>oi>, an animal. 



t Ann. des Sci. Nat. for Sept. 1828 and July 1836. f Symbol Physic. 



Zoological Besearches and Illustrations, Memoir 5. Cork, 1830. 



|| Phil. Trans., Part 2. for 1837. 



