50 T. H. MORGAN. 



on a dorsal projection, lie the four eyes equally dividing the 

 circumference. From the exterior each eye is seen surrounded 

 by pigment, generally of a yellowish-black color. The eyes 

 are extremely small and covered by thick chitin, rendering it 

 exceedingly difficult to get at the eyes either for sections or for 

 maceration. 



Fig. XX IV shows a side view of the anterior end of Phoxichili- 

 dium. It shows the shape of the cupola-like projection bearing 

 the eyes, two of which are seen on side view. The eyes of this 

 species are much larger than the eyes of either of the other two 

 Sea-Spiders, and for this reason were less difficult to manage, and 

 the following account will apply to the eyes of Phoxichilidium, 

 unless otherwise stated. "Alcoholic picro-sulphuric" solution 

 gave by far the most satisfactory results. The body was cut 

 across near to the eyes, and the portion containing the eyes fell 

 immediately into the killing fluid. After thoroughly washing 

 out the picric. acid the eyes were stained in hematoxylin and 

 afterwards cut in paraffine. 



We may start with a figure showing the whole eye removed 

 from the body, as seen in Fig. 30, Plate VII. The figure is of an 

 eye which had been sufficiently macerated to free it from the 

 surrounding tissue, removed in glycerine to a slide, and rolled 

 around until the innermost part of the eye was turned upwards. 

 The figure therefore shows the inner surface of the eye — that 

 part nearest to the center of the cupola. 



The pigment was, in handling, to some extent removed from 

 this part of the surface, so that by focusing beneath this another 

 layer of the eye could be seen. The figure shows the distribution 

 of the optic nerve to the eye, which comes directly from the 

 brain beneath the eye. The most important part of this figure 

 is the arrangement of the parts of the eye on each side of a 

 median line — the raphe. This runs through almost the whole 

 inner length of the eye as a somewhat irregular line from above 

 downwards, and is formed by the elements of the visual part of 

 the eye coming in contact from the two sides. Indeed, in this 

 figure almost seventy-five pairs of these elements are seen 

 arranged along each side of the raphe. 



The optic nerve, before it reaches the eye, breaks up into 

 several branches, and the branches enter the eye aloug its inner 



