43 



iciiiacles is probably ol' use as a j)i()lec(i(»n, like lliat uii 

 thf visceral hump. 



Tlie Jujes are a pair of organs situated on the outer 

 sides of the swollen bases of the tentacles (hgs. 4 and 2-3), 

 but their sha})e and })osition does not seem to be affected 

 by the expansion, contraction and motion of these organs. 



The eye is really a simple pit, lined by a continuation 

 of the general surface epithelium, part of which has 

 become modified in connection with the sense of light- 

 perception. This modified epithelium is found over a 

 shell-like area, which approaehes nearer to the opening 

 of the pit on the lower and outer than on the tentacular 

 and central side (tig. '25). In this modified epithelium 

 Ave find two kinds of cells (fig. 2(j) : -(1) Elongated sensory 

 cells, Avith swollen bases, and long clear processes directed 

 towards the surface; and (2) long Pigment cells sur- 

 rounding and filling up the interspaces between the 

 sensory cells. Each cell consists of [a] an internal 

 tapering region, fairly clear, and containing a nucleus 

 in its outer part; {]>) a broader middle region croAvded 

 A\-ith minute pigment-granules, and [c) a clear outer 

 region. The Pigment is black and resembles that of 

 the mantle. 



IVerve fibres, going lo (he optic nerve, are found 

 beneath this sensory epithelium. The cuticle is Avell 

 developed over the epithelium of the sensory region. The 

 eye of the Monobranch Docoglossa is more highly 

 dcA'eloped, its caA'ity is filled Avith a jelly-like substance, 

 and the opening is a narroAv slit. It is, therefore, almost 

 certain that the eye of Patella is degenerate, and this is 

 Avhat might be expected from the conditions of life, since 

 the head remains under the shade of the conical shell. 



The Otocyst, like the eye, first appears as a depression 

 in the epidermis at the side of the head. AVith further 



