THE PYCNOGONIDS. 53 



series of deeply stained rods — the bacilli, which occur regularly 

 from the top to the bottom of the eye, and it was these which 

 we saw in Fig. 30 arranged along each side of the middle line. 

 These bacilli are continuous with the cell-walls of the retinal 

 cells, which pass outwardly from the bacilli as far as the zone of 

 nuclei. The third and inner layer of the eye covers completely 

 the middle layer as far forward as the cells of the corneal hypo- 

 dermis, but its ending in the region of the hypodermis was not 

 well shown in the section from which this figure was taken. 

 This inner layer is composed of variously shaped cells containing 

 much dark pigment, but the shapes of these cells can only be 

 determined by maceration. 



It may be well to explain here that the cells composing the 

 middle layer correspond in number to the bacilli and cell bound- 

 aries shown in this ligure, and that they form a series of inverted 

 retinal elements, the length of which is almost as great as the 

 depth of the middle layer ; and, as we shall see later, there is a 

 nucleus to each of these elements. 



There remains a third plane in which I have cut sections of the 

 eye, viz. that passing at right angles to the length of the retinal 

 rods. A few sections of this series are shown in Figs. 34, 35 

 and 36. The first of these (34) is the second section from the 

 inside, the first section having cut off a slice of pigment. We 

 see the periphery surrounded by pigment, and in the center we 

 see the arrangement of the outer ends of the retinal cells where 

 they come in contact from the two sides. The raphe is here 

 clearly seen to be formed by the contact of the bacilli of the 

 two sides of the eye, and is formed as a zig-zag line by the inter- 

 locking of the bacillar ends of the retinal cells. Between the 

 bacilli the granular protoplasm of the cell is seen, which runs 

 almost to the tip, so that the bacilli are not formed at the inner 

 ends of the cells, hut along the side walls at the inner end. It is 

 also not to be overlooked that only the superficial layer of retinal 

 elements interlock at the surface, forming the raphe ; and, while 

 there are many other elements in the interior of the eye, these 

 do not seem to come to the inner surface, but lie just beneath 

 these superficial cells. At one point in Fig. 34, viz. in the lower 

 left-hand portion, the section passes a little below the superficial 

 bacilli, bringing to light the transversely cut ends of two of the 

 interior retinal elements. 



