COMPAEATIVE MOEPHOLOGY OF THE GALEODID.E. 347 



supply nourishment to the retinal cells and to the hypodcrmis, and fluid to the lens. 

 The ahstraction of the fluid from these canals causes the collapse of the retina and its 

 shrinking from the lens and from the circular iris-like fold of tlie hypodermis, in the 

 way shown in figs. 7, 8 (PI. XXXI.). 



Owing to the uusatisfactory state of preservation of the tissues, I have not succeeded 

 in making out the histology of the retina. The collapse of the fluid-channels above 

 mentioned, which perhaps kept the retinal elements distinct, in all cases confused the 

 field. Certain important points were, however, clear : 



1. There was no developed vitreous body, the hypodermis-cells (%) l)cing confined to a 

 single thin layer of closely-packed cells with large nuclei, separated from the distal 

 ends of the retinal cells by a very fine membrane. 



2. The clear ends of the retinal cells, which were very short in the axis of the eye, 

 but longer round its j^eriphery, showed no difi'erentiation into rods. 



3. A short way below the commencement of the pigment-layer is found a zone of large 

 nuclei, wliich are apparently the nuclei of the retinal cells. I could make out no 

 retinulation or grouping of retinal cells round a rhabdom. I could indeed find no 

 traces of rhabdoms, and from the very crooked courses of the retinal elements in the 

 axial portion of tlie eye I doubt whether any such could have been present. It appeared 

 to me as if the retinal cells ran singly, closely entwined by strings of pigment-granules, 

 which, liere and there, were clumped together. These pigment-clumps may, in some 

 cases, indicate the presence of the nuclei of the pigment-cells, in the pseudopodia of 

 which the strings of smaU pigment-granules are probably enclosed. 



4. While the hypodermis-cells secreting the lens are naturally clear and free from 

 pigment, those which form the iris-like fold, and which from thence line the rest of the 

 ocular tubercle, are closely packed with very large round pigment-granules. 



A comparison of the eye of Galeodcs with the homologous eyes in Scorpio on the one hand (Lan- 

 kester and Bourne, 45), and of the Spiders on the other (Bertkau, 18), shows how little reliance can be 

 placed on eyes in establishing points of relationship. It is not too much to say that, according to the 

 descriptions given, the median eyes of these thi'ce Arachnids, the Scorpions, Spiders, and Galeodidse, 

 are built on entirely different plans. A similarly complete difference between the lateral eyes of the 

 Pseudoscorpions and those of the Scoi'pions has also been pointed out (10). 



(2) T//e Vestigial Lateral Ei/es. — The most interesting point about these eyes is 

 their extreme irregularity. These lateral eyes occiu-red in all specimens of Galeodidse 

 which I have examined, sometimes in two pairs. They lie under the remarkable area 

 at the sides of the cephalic lobes, and thus look forward and downward. Tliis fact 

 again suggests that these areas are quite secondary modifications developed for the 

 purpose above described (jj. 321) since the lateral eyes left the ocular tubercles. 



These lateral eyes vary in size and shape, the anterior being sometimes long and 

 elliptical, while the posterior is small and round ; sometimes they have run together to 

 form a long narrow single eye (PI. XXIX. fig. I, le, Rhax melaiia). The lees has eutu-ely 

 atrophied, and the eyes are inserted into j)its on the inner side of the thick cuticle (14). 

 It is on this account that I call the eyes vestigial, although, from the develojiment 



46* 



