298 ANATOMY OF TEH LAMELIBRANCHIATA. 



providing for the gradual growth and change of an internal 

 skeleton by the deposition and subtraction of its compound 

 particles. 



CILIA. 



The branchice, tentacles, edges of the mantle, extremity of 

 the foot, internal surface of the siphons, &c. are, in these ani- 

 mals, more or less covered with vibratile cilia, or seta, for the 

 purpose of producing currents in the water. In examining, 

 under the microscope, the intestinal tube of the small British 

 species of Chiton, taken from the living animal, the author 

 observed a peculiar motion on the external surface of its pos- 

 terior part. This arises from the passage of the intestine 

 through the secreting organs, which lie between the viscera 

 and the foot. The same has been observed on the intestine 

 of the Cephalopoda, * which also passes through the secreting 

 sac, and also on the appendages to the veins of those animals. 

 The water appears to enter the secreting cavities from the 

 existence of cilia. The existence of the curious appearance 

 produced by the existence of the cilia, was noticed by Mul- 

 ler, 2 Heyde, 3 Piquemare, 4 Leuwenhoek, 5 Lister, 6 Baker, 7 

 &c. By some of these, from the imperfection of their instru- 

 ments, the appearance was attributed to the circulation. — 

 RaspaiP has shown that many of the animalcules described 

 by authors, are merely vibratile parts of higher animals ; and 

 many more instances of the same mistake might be given. — 

 Dr. Sharpey 9 has shown that some of the higher Vertebrata 

 are ciliated, as may be seen in the branchice of the tadpole. 

 Swammerdam 1 and Cams 2 in the embryo of the Paludina, 

 Stiebel 3 and Hugi 4 in that of the Lymnceus, Grant 5 in that 

 of the Buccinum, and Leuwenhoek, 6 Home, 7 and Cams 8 in 

 that of the Unio, have noticed a rotatory motion of the em- 

 bryo in the ovum, evidently owing to the action of these cilia, 

 though Cams does not attribute it to this cause, and Home 



1 Professor Grant notices "a remarkable peristaltic action" of the glands 

 of the Loligo. Jam. Journal, 1826. 



2 Hist. Vermium, &c. 3 Anatomia Mytuli. 4 Ency. Meth. Actinia. 



5 Arcana Naturae. 6 Exercit. Anatomic 7 On the Microscope. 



8 Bull. Sciences Nat. 1827; Isis, 1829; and Ann. Sci. d'Observation, 1. 

 9 Edin. Med. & Surg. Journ. 1830. In a paper read before the Linnean 

 Society, in 1834, the author lays claim to a few observations previously 

 made by Dr. Sharpey, and recorded in the paper here referred to, in the 

 Med. & Surg. Journ., which the author had not seen. 



1 Bibel der Natur. 2 Von den iEusseren Lebensbedingungen, &c. 1824. 



3 Arch, der Physiol, vol. ii. 4 Isis, 1823. 5 Edin. Journ. 1828. 



6 Arcan. Natur. 7 Croonian Lecture. 8 Neue Untersuchungen, &c. 1832 



