228 THE CEPHALOPHORA. $ 202. 
de Vordre des Opisthobranches (Milne Edwards), Tectibranches, Nudi- 
branches, Inférobranches (Cuvier) ; Ann. d. Se. Nat. IX. 1848, p. 172, XI. 
1849, p. 74. 
ree and Hancock. A Monograph of the British Nudibranchiate Mol- 
lusca with figures of all the species. Part I. 1844. Part V.1851. Un- 
finished. [This fine work contains very valuable anatomical details and 
includes Hancock’s contributions upon these animals given also in the Ann. 
of Nat. Hist.] 
On the Anatomy of Oithonia, in the Ann. of Nat. Hist. IX. 
1852, p. 188. 
Hancock and Embleton. On the Anatomy of Eolis (Contin.). Ann. 
Nat. Hist. 1848, I. p. 105, also 1849, III. p. 183. 
Hancock. On the olfactory apparatus of the Bullidae. Ibid. IX. 1852, 
p. 188. 
On the Anatomy of Doris, in the Philos. Trans. 1852, Part. 
Ii. p. 1. 
Souleyet. Mémoire sur le genre Acteon d’Oken, Journal de Concholo- 
gie, 1850, No. I. p. 1. 
Leidy. The Terrestrial air-breathing Mollusks of the United States, &. 
Described and illustrated by Amos Binney. Edited by Aug. A. Gould, 
M.D. 2 vol. Boston, 1851. Special Anatomy by Joseph Leidy, M.D. 
[For beauty of execution Leidy’s drawings are unsurpassed. ] 
Leydig. Ueber Paludina vivipara: im Beitrag sur naheren Kenntniss 
dieses Thieres in embryologischer, anatomischer und histologischer Bezie- 
hung; in Siebold and Kélliker’s Zeitsch. IL. 1850, p. 125. 
Anatomische Bemerkungen tiber Carinaria, Firola und Amphi- 
cora. Ibid. IIT. 1852, p. 325. 
Koren and Damelssen. Bitrag til Pectinibranchiernes Udviklingshisto- 
rie, Bergen, 1851, or its Transl. into the French, in the Ann. d. Sc. Nat. 
XVIII. 1852, p. 257. 
Gegenbaur. Beitrage zur Entwickelungsgeschichte der Landgastropo- 
den, in Siebold and Kolliker’s Zeitsch. III. 1852, p. 871. 
Bau der Heteropoden und Pteropoden. Ibid. IV. 1853, p. 
334. 
Moguin-Tandon. Histoire naturelle des Mollusques terrestres et fluvi- 
atiles de la France, 1847, avec un Atlas de 25 Planches, &c. Anatomie 
de Ancyle fluviatile, in the Jour. de Conchol. 1852, No. I. p. 7, No. IL. p. 
121, and No. IV. p. 337. 
Rang and Souleyet. Histoire naturelle des Ptéropodes, Paris, 1852. 
CHAPTER I. 
CUTANEOUS SYSTEM. 
§ 202. 
The cutaneous envelope of the Cephalophora consists of a dense dermis, 
of a cellular structure, often containing pigment matter which is free 
or in cells. It is covered with a delicate ciliated epithelium, which, with 
