The developed eye in the dibranchiate Cephalopods consists of a transparent cornea, which may or may not be closed over the front of the lens. Behind the cornea is a narrow chamber (the anterior optic chamber) which is continued for three parts round the whole circle of the eye, and into which project the front portion of the lens and the folds of the iris. Throughout its whole extent, the anterior optic chamber is lined by the integument, the portion of which on the inner side is the choroid. The lens is divided into an outer and inner segment by a thin membrane, and is supported by the ciliary body which forms a continuation of the retina. The main portion of the lens lies within the posterior optic chamber, at the back and sides of which is found the retina (Grenacher). There can be no doubt that the Cephalopoda use their eyes to observe, but there is nothing to show that any other Mollusca use their eyes for this purpose, the sense of smell in their case largely taking the place of visual observation. Madame Jeannette Power once saw[286] the _Octopus_ in her aquarium holding a fragment of rock in one of its arms, and watching a _Pinna_ which was opening its valves. As soon as they were perfectly open, the Poulpe, with incredible address and promptitude, placed the stone between the valves, preventing the _Pinna_ from closing again, upon which it set about devouring its victim. The next day the Poulpe was seen, after crushing some _Tellina_, to stretch himself down close by a _Triton nodiferus_, and watch it attentively. After four hours the _Triton_ emerged from its shell, when the _Octopus_ sprang upon it, and surrounded it with its arms.