188 



SENSES SIGHT. 





opinion may be correct, I cannot say ; * but a physiologist 

 of great ingenuity has inferred that in the bivalves in ques- 

 tion there is a sense analogous, at least, to that of ordinary 

 vision, from their quick and varied motions, and from the 

 fact that the Trigoniae, in their attempts to escape from a 

 boat, leap in a definite direction, as Mr. Stutchbury had 

 witnessed, f 



The great majority of Fig. 34.+ 



the Pteropods, though 

 apjDarently influenced 

 by light, and a few 

 marine naked Gastero- 

 pods, are eyeless ; § but 

 organs which have been 

 generally considered as 

 serving the purposes 

 of vision, have been 

 bestowed on all other 

 mollusca. There can 

 be no question of their 

 function in the Cepha- 

 lopods, for in them the 

 eyes are very large, and 



similar, in all essential points, to those of vertebrate ani- 

 mals. They are two in number, one on each side of the 



* " Each of tliesc ocelli possesses a cornea, lens, choroid, and nerve : they 

 arc, without doubt, organs of vision." — Garner in Mag. Nat. Hist. n. s. iii. 

 128. — " Will has instituted researches on the eyes of the Conchifera He 

 found them to be very highly organised. Besides Pccten, Sphondylus, and 

 Ostrea, he found tliem also in Pinna, Area, Pectunculus, Mytilus, Cardium, 

 Tellina, Mactra, Venus, Solen, Pholas, sometimes in vast numbers." — Re- 

 ports on Zoology for 1844, p. 439, printed for the Ray Society, Lond. 1847. 



t Carpenter's Gen. and Cump. Phys. pp. 98,99. 



X The figure is a view of the eye of Octopus vulgaris, copied from Cuvier. 

 a a, A cellular and muscular tunic, the latter for opening the lids; hh, the 

 conjunctiva ; c, another tunic, enveloping the globe of the eye, and a pouch 

 situated behind it (e), containing (/") the optic ganglia, and the glands 

 which surround it {g). The pouch (e) is a transparent membrane, which 

 occupies all the space between the globe of the eye and the tunics which go 

 to its lids ; so that the former actually fills only about a third of the greater 

 globe, which, at first view, appears to be the eye itself, h li, The external 

 coat of the proper eye, perforated with an infinite number of minute holes, 

 for the passage of the filaments from the optic ganglion ; and i, another coat, 

 formed apparently by the expansion and netting of these nervous filaments. 

 m, The crystalline lens. — I may also refer to a description and figure of 

 Loligo sagittata in the Edinb. j'ourn. Nat. and Geogr. Sc. iii. 286. 



§ The existence of eyes in Doris and Goniodoris, — genera that had hither- 

 to been described as entirely devoid of these organs, — -has been proved by my 

 friends Alder and Hancock, of Newcastle. They are to be most distinctly 

 observed in young individuals. — Ann. Nat. Hist. i\. 31. 



