EXPLANATION OF THE PLATES. 301 



66. (Esophageal ring of Sepia otticinalis from the back. 



(Mihie Edwards.) gbi, gbs, inferior and superior 

 buccal ganglia ; 6, arm nerves ; op, optic nerve ; o e, 

 gullet ; g v, visceral ganglion ; g c, cerebral ganglion, 10 



67. Schematic figure of the nervous centres of a geophilous 



pulmonate. a, cerebral ganglia; 6, pedal ganglia; c, 

 visceral ganglia ; d, stomato-gastric ganglia ; /, con- 

 nectives uniting the subuesophageal to the visceral 

 ganglia; h, connectives uniting the suboesophageal 

 to the stomato-gastric ganglia; o, otocysts, . tl, T2 



68. Schematic figure of the nervous system of Chiton 



cinereus, Linn, a, anterior curve formed bj- the com- 

 missures of the pedal and branchial trunks ; &, antero- 

 superior pharyngeal ganglia ; c, small postero-superior 

 phar3aigeal ganglia ; cZ, antero-inferior pharj-ngeal 

 ganglia ; e, vascular ganglia ; w, branchial nerves ; 

 p, nerves of the pedal disk with their transverse com- 

 missures, ......... 12 



69. Nervous system of Anodonta. a, buccal ganglia ; 6, 



pedal; c, branchial ganglia (Fischer), . . . tS 



Plate 6. 



TO. Section of eye of Sepia oflScinalis. (After Hensen.^ k, 

 Cephalic cartilage, k', Eyelid cartilage, iv k, White 

 bodies, c. Cornea. Z, Lens. ^ i, Argentea interna. 

 A e, Argentea externa, k, Ej^e cartilage with the 

 thick sequatorial cartilage, i k, Iris cartilage, g, 

 Optic ganglion. R e, Retina externa. B i, Retina 

 interna, p, Pigment, h y, Hyaloidea. c, Ciliary 

 bodies. . . . . . . . . .15 



IL Eye and olfactory organ of Sepia. (Zernofli".) a. Olfac- 

 tory organ, n, olfactory nerve. 6, eyeball, c, optic 

 ganglion, d e f, principal ganglia of the brain, g. 

 anterior nerve of siphon, h, nerves of the mantle 

 ganglion, k, sympathethic nerve. Z, nerves leading 

 to the cephalic ganglion and arms, m, nerve of the 

 e3'e. n, olfactory nerve, o, eye cavity, p, skin, 15, 18 



12. Head of Glandina fusiformis, Pfeiflfer. a, eyes ; &, inferior 



tentacles ; c, labial palpi ; d, buccal orifice, . 14, 15 



13, 14. Schematic figures of the eye of Helix pomatia, show- 



ing the mode of retraction within the tent!icles. a, 

 external wall of the tentacle ; 6, crystalline lens ; d, 

 retractor of the lens ; /", ocular chamber ; g, retina; 

 k, retractor muscle of the ocular globe ; p, optic gan- 

 glion ; o, optic nerve, . . . . . . 11 



