152 ANATOMY AND LIFE HISTORY OF MOLLUSCA. 



subject readers must be referred to the observations on the 

 development of the Cephalopoda by Dr. Ray Lankester in the 

 " Quarterly Journal of Microscopical Science " for 1875, xv., p. 87. 



There are many peculiarities in the eyes of Cephalapoda which 

 it would be beside my purpose to enter upon here ; but I may 

 mention that the cornea is absent from the eye of Nautilus as 

 well as the lens. The integument which replaces the cornea has 

 a pupil-like orifice which leads into the interior of the bulb. This 

 integument is perforated in the adult Octopus and the anterior 

 surface of the bulb is bathed by water. The space which 

 communicates with the exterior is not only continued through the 

 optic cleft as far as the lens, but also extends more or less around 

 the bulb. The base of the bulb is formed by a cartilaginous 

 capsule. Around the pupil this becomes converted into the 

 cartilage of the iris. Outside and behind this optic capsule (let it 

 be observed that we are now dealing with an adult eye and not 

 entirely with the section) is the ganglion of the optic nerve in the 

 periphery of which there is the whitish organ which projects more 

 or less forwards. Behind this is a layer of muscles and then a 

 silvery membrane (aryentia externa) reaching to the edge of the 

 pupil, investing the bulb on its inner face. Internally is the 

 argentia interna. The nerves pass by pores in the capsule to the 

 retina. This is divided into an internal portion containing the 

 perceptive elements, separated from the outer portion by a layer 

 of pigment. The substance of the above description of the adult 

 eye is taken from Gegenbaur (Comp. Anat.) and Ray Lankester. 



Especial attention is called in this section to the line of division 

 between the internal and external layer of rods of the retina. 

 The ends of the internal layer project through the pigment 

 membrane in a series of remarkable bodies and there seems to be 

 no connection between them and an external layer of nerve 

 substance. This will be the subject of further investigation. 

 Finally it may be mentioned that the "ciliary body" is a series 

 of lamellse which invest the edge of the lens. 



I fully anticipate that this novelty of eyes in the shell of Patella, 

 and, as I shall show of many other shells of different genera, will 

 only make its way with difficulty, especially when it is remembered 

 that such an experienced naturalist as Mr. Mosely searched for 

 them in vain in a European species of the same genus. Moreover 

 he expressly states that he believes that Chitonidse is the only 

 family where the arrangements of the peculiar structure render 

 such organs possible. Therefore I warn observers beforehand of 

 the great difficulty attendant upon the observation of these eyes. 

 They are much more minute than those in the shell of Chiton, 

 and they are so often hidden in the rough inequalities on the 

 surface of the shell, as well as by foreign matters and the corrosive 



