THE PYCNOGONIDS. 51 



surface and along a line corresponding approximately to that 

 of the raphe. The nerve branches disappear in the pigment 

 covering the inner surface of the eye, and cannot be followed 

 farther. 



If we make a section in a horizontal plane through the cupola, 

 so that all of the eyes are cut transversely to their longest diam- 

 eter which runs from above downwards, we obtain a figure 

 shown in 31. The four eyes are about equally distant from each 

 other. In front of each the chitin is greatly thickened to form 

 a lens ; beneath this the corneal hypodermis is very much thick- 

 ened ; under the corneal hypodermis is a cup-shaped mass com- 

 posed of two layers — 1st, a light layer containing nuclei, and 2d, 

 a layer of pigment surrounding the first. The entrance of the 

 nerve is shown in some of the eyes at their inner, middle part. 

 If we examine one of these eyes under a higher power of the 

 microscope, we obtain such a figure as is shown in Fig. 32. The 

 chitinous lens is well shown here, and the great increase of its 

 thickness over the eye is very marked. The ectoderm of the 

 body, the so-called hypodermis, also undergoes a great change in 

 the region of the eye. The cells are much longer, have con- 

 spicuously large nuclei, and tapering away at their inner ends 

 into fine processes which run out to the two sides of the eye. 

 The whole arrangement of these corneal-hypodermal cells — 

 lentigen cells — is markedly bilateral, as seen in Fig. 32. 



Immediately under the lentigen cells lies the middle layer of 

 the eye. This is the retinal part of the eye, or that part sensi- 

 tive to light. Immediately under the corneal hypodermis this 

 middle layer of the eye shows a meshwork of fiber-like pro- 

 cesses, which are probably interlacing and anastomosing nerve 

 fibrils. Passing inwardly, there next follows a zone containing 

 conspicuous nuclei and large vacuolated spaces. There next 

 comes a zone which contains slightly stainable, rounded bodies 

 slightly smaller than the nuclei. Lastly, in the bottom of this 

 cup-shaped middle layer is a portion of the middle layer which 

 stains more deeply than the rest of the middle layer, and 

 radiating through this from the bottom of the cup outwards 

 are several deeply stained (drawn black in the figure) rod-like 

 bodies or bacilli. Corresponding somewhat to the intervals 

 between the bacilli, the middle layer is indistinctly split up into 



