EEPORT ON THE PYCNOGONIDA. 123 



Plate XXL, I figure a longitiidinal 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 abeady 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 reaUy 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 rucUmentary 

 ceUs represented by nuclei. Of a distinct row of vitreous body ceUs, like those figured 

 and described by Grenacher {he. cit.) and Graber,^ I obsei-ved nothing. Nor do I 

 believe that Dohrn's assertion is right, that in the eyes of the Pycnogonida the retina 

 is derived from the epithehum 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 (PI. 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-hke appendages. In these 

 retinal elements I failed to observe any trace of the presence of nuclei. The thread- 

 like appendages of the rods extend tiU they reach the cuticular lens. A prajretinal 

 lamella, which, according to Graber, is characteristic of the stemma of the tracheate 

 Arthropods is not visible. Between the rod-forming elements numerous ganglion ceUs 

 are observed in the form of distinct rounded ceUs. 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 gangUon ceUs 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 verticaUy through about the middle of the eye 



1 Gral^er, V.— Ueber das imicomeale Tracheaten-imd speciell das Arachnoideen-und Myiiopoden-Aiige. Archiv. 

 f. Miki. Anatomic. XVII. 1880, p. 58-93, PI. v.-ni. 



