756 William Patten, Eyes of Molluscs and Arthropods. 



Fig. 135. Same, with cross section, from the anterior ocellus of a spider. 



Fig. 136. The same, from ocellus oi Scurpio. 



Fig. 137. The same, from posterior ocellus of a Spider. 



Fig. 138. The same, from the compound eye of Insects and Crustacea. 



Fig. 139. Two retinophorae from the retina of Cephalopods , with the ganglionic 

 cell g.c, producing the external fibres of the rods, and the axial nerve 

 fibres, ax.n.\ the body of the retinophora (or retinal cell ofGRKNACiiER), 

 contains two nuclei. 



Fig. 140. Two retinophorae with their ganglionic cells, from the retina o{ Pecten, 

 showing the loops of the axial, and external, nerves of the rods, the two 

 nuclei of the retinophorae , and five characteristic forms of ganglionic 

 cells; b.m. basal membrane or septum of the eye; x. a nerve fibre termiu- 

 ating on the small ganglionic cell (/-cJ^; z. andy. two methuds of nerve 

 endings upon the cell wall of the retinophorae. 



Fig. 141. Ancestral Arthropod eye. 



Fig. 142. Ej^e of Peripatus. (Modified from Carrière.) 



Fig. 143. Ocellus of Myriapod. 



Fig. 144. Same of larvai Insect. 



Fig. 145. Ocellus oi Scorpio; ouly one ommatidium is represented. 



Fig. 146. Posterior ocellus of Spiders. 



Fig. 147. Diagram of compound eye, constructed according to Grenaciier. 



Fig. 148. Diagram of compoimd eye to illustrate its origin at a modified single 

 ocellus (compare fig. 146). 



Fig. 149. Diagram of the eye oiPecten to show the formationofasecondimage over 

 the first; the rays of light from a.h. form a curved, inverted image upon 

 the layer of rods, x.y. ; but the rays of light diverging from x.y. are reflect- 

 edby the curved mirror ay. (the argentea), and come again to a focus ata-. 

 y.\ with the microscope one sees the less distinct, second image at x.y.K 



Fig. 150—152. Three drawings to show the supposed methodby which the eyes of 

 Pecten originated ; fig. 150 an open cup, the retineum of which consists 

 of rodless retìnulae, arranged in two layers, jjg.^ — -, and of colorless and 

 double retinophorae. Fig. 152, the cup has closed, and the anterior wall 

 of the vesicle has become most highly developed, while the rods of the 

 posterior wall, rhA, nearly disappear; the basai membrane, fig. 150, h.mJ 

 forms the septum. Fig. 152, some of the nerve fibres have united to form 

 two brauches, those which supplied the floor of the primitive cup remain 

 isolated 7ì.fA and probably give rise to the fibres, with spindle-shaped 

 swellinfis, which penetrate the sclerotica, and tapetum; PI. 30, fig. 39, 

 X. ; the rods of the posterior wall of the optic vesicle form the vitreous 

 network of the adult, v.r. 



Fig. 153. Diagram representing the transformation of a neuro-epithel celi, b., with 

 its nervous Prolongation, x. , into abipolar ganglionic one, e., and finally into 

 a multipolar ganglionic one/. * and/.-; a., is a myo- epithel cell with its 

 root-like and radiating fibres which unite to form a basai membrane ; ce. 

 is the corneal cuticula, and r.c. the retinidial cuticula, containing the retia 

 terminalia of the hypodermic nerves; g., and /*., represent modifica- 

 tìons of hypodermic cells, with their retia terminalia, to form the omma- 

 tidia of an invaginate and compound MoUuscan eye. 



Druck von Breitkopf & Härtel iu Leipzig. 



