346 ME. H. M. BERNARD ON THE 



compared with the size of the ocular tubercle, and somewhat tilted so as to look side- 

 •oays, their axes making together an angle of 90". In the genus Bhax (PI. XXVII. 

 fig. 6) the lenses are small and lie rather wide apart, looking almost directly upward. 



The lens is formed by the sudden thickening of the cliitinous lamina? of the cuticle, 

 and is thus itself laminate *. As it stains deeply, it is probable that these layers are 

 largely protoplasmic or permeated with fluid in the interest of transparency. The 

 outermost layer of the chitin is generally wrinkled (fig. 9), as if it had shrunk by the 

 al)straction of such a fluid. The whole eye, indeed {I. e. the soft parts), is abun- 

 dantly provided with canals for the free circulation of fluids through all the tissues 



{fig. 8, Ic). 



In the angle between the globular lens and the cuticle from which it is developed a thick 

 fold of pigmented hypodermis forms a kind of iris. It is apparently rather more pro- 

 noimced than Leydig's ' iris-artige Giirtel ' in the eyes of Spiders, which was only a ring 

 of pigmented hypodermis. In Galeodes it is a thick and very definite fold arranged right 

 round the retina (PL XXXI. figs. 7, 8, 9). Its apparent function will be presently 

 described. 



The general character of the eye can be obtained from the figures. The most 

 remarkable featui^e is the thinning away of the retina in the axis of the eye, and its 

 great development roimd the periphery. The i-elative measttrements were as follows : — 

 greatest depth of lens 25, depth of retina in the axis of the eye 3, at the periphery 

 (posterior) 20, (anterior) 12. 



The whole of the soft parts of the eye are enclosed in a well-developed connective-tissue 

 membrane, which stretches across below the ocular tubercle (PI. XXXI. figs. 7, 8, m). 



The optic nerve enters the postero-median region of this ocular chamber, and 

 immediately swells into a ganglionic mass. From the dorsal surface of this ganglion 

 the fibres bend sharply to right and left to run in all directions to the retina-cells. 

 Pitrment-cells, with rather large round granules, begin to accompany them almost 

 immediately they leave the ganglion, like single or double strings of beads. 



The space aroimd this ganglion, and for some way up at the sides of the retina, i. e. 

 between it and the chitinous walls of the ocular tubercle, is filled with blood-cells and 

 traversed by connective-tissue fibres. High tip round the lens the circular iris-like fold 

 of the hypodermis is filled by a close reticulum of coarse threads like a sponge {sp). 

 This spongy cushion, which completely surrounds the lens in the angle between it and 

 the chitinous body-wall, may perhaps have something to do in effecting or regulating, 

 by means of fluid pressure, slight movements of the eye. Prom the flexibility of the 

 cuticle, close round the lens (fig. l,fl), some slight movements seem possible, and I 

 have found no other mechanism for the purpose. 



From the fluid space beneath the retina and around the ganglion an enormous number 

 of channels, anastomosing freely with each other (fig. 8, Ic), run up between the 

 retinal cells as far as the hypodermal cells which secrete the lens. These, no doubt, 



* Bertkau(i8) says that in Spiders there are more laminae in the lens than in the cuticle. This is not the 

 case in Galeodes ; so far as it is possible to count the lamina? accurately, the numbers agree. 



