124 THE VOYAGE OF H.M.S. CHALLENGER. 
(Pl. XXI. fig. 3). When the same (tangential) section passes through the lateral part 
of the eye another structure is observed (Pl. XXI. 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 dropped, are observed in it. A horizontal section of one of the eyes of Mymphon 
strémii (Pl. 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 (2), is observed laterally. The dimen- 
sions of the ganglion cells placed in the meshes of this reticular tissue in W% ymphon 
brachyrhynchus are almost the same as those observed between the retinal rods; but in 
Nymphon strémii 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 Nymphon brachyrhynchus axe 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 Pyenogonids may be summarised as follows :— 
(1.) A vitreous body, developed out of the cuticular epithelium (hypodermis), does 
not exist. 
(2.) The epithelium cells 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 preretinal 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 ig 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 
