124 THE VOYAGE OF H.M.S. CHALLENGER. 



(PI. XXI. fig. 3). When the same (tangential) section passes through the lateral part 

 of the eye another structure is observed (PL XXL fig. 2), viz., a mass of reticular tissue, 

 with numerous ganglion cells in its meshes, not unlike but a little smaller than those 

 between the rods of the retina. Empty cavities, from which, perhaps, ganglion cells 

 have cbopped, are observed in it. A horizontal section of one of the eyes of Nymiihon 

 stromii (PI. XXI. fig. 1) shows the arrangement of these parts in the interior of the 

 eye. The middle part is that occupied by the retinal rods, which here have large 

 ganglion cells at their extremities, and a distinct mass of reticular tissue, separated 

 from the retinal rods by a thin membrane (?), is observed laterally. The dimen- 

 sions of the ganglion cells placed in the meshes of this reticular tissue in NympJion 

 hrachyrhynchus are almost the same as those observed between the retinal rods ; but in 

 Nymphon stromii the ganglion cells which are found at the extremities of the retinal rods 

 are much larger. In regard to the minute structure of these ganglion cells I have hardly 

 any observations worthy of being mentioned. The cells are always furnished with a 

 distinct nucleus, and their contents, as a rule, are granular. Those I observed between 

 the rods of Nymiyhon brachyrhynchus are furnished with one filament directed towards 

 the lens. 



The conclusions I have arrived at with regard to the anatomy of the organs of vision 

 in the Challenger Pycnogonids may be summarised as follows : — 



(1.) A vitreous body, developed out of the cuticular epithelium (hypodermis), does 

 not exist. 



(2.) The epithelium ceUs are present under the lens of the eyes in the same 

 condition as under the cuticula in general. 



(3.) The retina consists of distinct rods and ganglion cells. Numerous ganglion cells, 

 placed in the meshes of a reticular tissue, form a mass, which encloses the interior of the 

 eye occupied by the rods. 



(4.) The ends of the retinal rods reach the cuticular lens. A prgeretinal interlamella 

 seems not to exist. 



(5.) The retinal rods can not be considered as having resulted from transformed 

 hypodermic cells. 



(6.) The retinal rods have two parts — an innermost thicker part and a filamentary 

 appendage. 



(7.) The eye is surrounded by a chitinous cuticula. 



4. Alimentary Canal and its Appendages. — I only occasionally got preparations of 

 the alimentary canal ; therefore what I have observed in regard to this organ is far 

 from exhaustive. 



Physiologically, this is perhaps the most interesting organ of all, and, morphologi- 

 cally, its signification is by no means small, as its structure has, along with the number 



