362 BRACHIOPODA. 



pedunculated eyes. After keeping several of the above for some 

 days in sea- water, they threw off their exuvia, and, becoming firmly 

 adherent to the bottom of the vessel, were changed into young 

 Barnacles ; and the peculiarly formed shells with their opercula 

 were soon distinctly formed, while the movements of the cirrhi, 

 although as yet imperfect, were visible. As the shell becomes 

 more complete, the eyes gradually disappear, the arms become 

 perfectly ciliated, and an animal originally natatory and locomotive, 

 and provided with a distinct organ of sight, becomes permanently 

 and immoveably fixed, and its optic apparatus obliterated. 



Similar results were obtained by watching the developement of 

 the pedunculated type of Cirripeds* (Lepades), many of which 

 were proved in their earliest form to resemble different kinds of 

 Monoculi, and to be possessed of the capability of locomotion. 



CHAPTER XX. 



BRACHIOPODA-J" (Cuv.) ; PALLIOBRANCHIATAJ (Owen). 



(398.) THE next class of Mollusca which presents itself for our 

 consideration was named by Cuvier on account of the remarkable 

 character of the organs by means of which the animals composing 

 it procure the food destined to their support. These instruments 

 consist of two long spiral arms placed on each side of the mouth, 

 that in many species can be unrolled to a considerable length, 

 and protruded to some distance, in search of aliment. The above 

 character, however, taken by itself, would scarcely warrant us in 

 considering the creatures before us as forming a separate class of 

 Mollusca ; but when, in addition to this remarkable feature in 

 their organization, we find that they possess a respiratory appa- 

 ratus peculiar to themselves, and differ widely from all other bi- 

 valves in almost every part of their structure, we feel little hesita- 

 tion in continuing to regard them as distinct, and devoting the 

 present chapter to an investigation of their anatomy. 



* Phil. Trans, for 1835, page 355. 



j- BgctX'*" 1 ) an arm ; jrayj, xobot, afoot. 



$ Pallium, a mantle ; branchiae, gills. This name, originally proposed by Mons. 

 de Blainville, notwithstanding his belief that the spiral arms were the organs of respira- 

 tion, has since been proved by the researches of Professor Owen to be strictly appro- 

 priate to the class. 



