REPORT ON THE PYCNOGONIDA. 123 
Plate XXI., I figure a longitudinal section of one of the eyes of this species; and in the 
same figure the place occupied by the outer surface of the eye of the other side is indicated 
(a). This outer surface is invested by a thin chitinous cuticle, which is minutely (longi- 
tudinally) striped ; round the circumference it is in connection with the chitinous skin 
of the animal. The inside of this wall is covered with pigment, and it is in this bed of 
pigment that the union of the fibres of the optic nerve with the elements of the retina 
takes place. I have already spoken above about the manner in which the optic nerve 
penetrates the eye. I sometimes got preparations, which made me believe that the optic 
nerve reached the outer integument of the oculiferous tubercle, at a considerable distance 
below the eyes, and that it ran along this wall and penetrated the eye where it is in 
connection with this integument ; this, however, is not really the case. Numerous 
separate nerve fibres reach the under surface of the eye; they then penetrate its cuticle, 
and in one of my preparations I observed distinctly, that they are in direct connection 
with the rods of the retina. 
In the interior of the eye there is a retina, but there is no distinct vitreous body. 
I observed that under the thickened cuticula which forms the lens of the eye, just as 
everywhere else, the epithelium (hypodermis) of the cuticula is formed of rudimentary 
cells represented by nuclei. Of a distinct row of vitreous body cells, like those figured 
and: described by Grenacher (Joc. cit.) and Graber, I observed nothing. Nor do I 
believe that Dohrn’s assertion is right, that in the eyes of the Pycnogonida the retina 
is derived from the epithelium cells (hypodermic cells). This retina consists of rod- 
forming elements and of ganglion cells. Those parts of the rods which are directed 
towards the fibres of the optic nerve are thicker and terminate abruptly (Pl. XXI. fig. 4), 
bearing at the other extremity a long and filamentary appendage; while in other 
preparations the retina elements which I isolated show the form figured in Plate XXI. 
fig. 5,—viz., rods which imperceptibly pass. into thread-like appendages. In these 
retinal elements I failed to’ observe any trace of the presence of nuclei. The thread- 
like appendages of the rods extend till they reach the cuticular lens, A preeretinal 
. lamella,- which, according to Graber, is characteristic of the stemma of the tracheate 
Arthropods is not visible. Between the rod-forming elements numerous ganglion cells 
- are observed in the. form of distinct rounded cells. I did not observe whether or not 
they were really in connection with the filamentary appendages of the rods; but having 
isolated from one of the preparations the rods, as figured in fig. 5, I found that the rod 
passes into the filamentary appendage. Probably the. ganglion cells have also fila- 
mentary appendages, which pass between the filaments of the rods. In this respect 
' therefore my opinion is intermediate to those of Grenacher and Graber. This structure 
is observed when the section passes vertically through about the middle of the eye 
1 Graber, V.—Ueber das unicorneale Tracheaten-und speciell ‘das Arachnoideen-und Myriopoden-Auge. Archiy, 
f, Mikr. Anatomie. XVII. 1880, p. 58-93, PI. v.—vii. 
