Eyes of Mollnscs and Arthropods. 755 



Fig. 129. Outer end of one of the crystalline cone cells (retinophora), isolated b)»- 



niaceratlon, showing thc system of externa! nervo fibres (Paiaemon). 

 Fig. 130. The same seen from the abaxial surfixce. 

 Fig. 131. Style of Paiaemon (macerated), with the externa! nerve fibres. 

 "Fig. 132. Same seen in optica! section, showing axial nerve with lateral fibrillae. 



Fiate 32. 



ax.7i. axial nerve. p^.i,-,3 first, second and third circie of 



hc. bacillus. pigment ceüs. 



b.in. basal membrane. rf. retinophorae. 



c.c. cornea! cuticuia. r/".' innerraost ends of crystalline 



C.C.C, crystalline cone ceüs. cone ceüs, or retinophorae. 



chi/. cornea! liypodermìs. rh. rod, or crystalline cone. 



ex.li. externa! nerve fibres. rt. retinula. 



g.c. ganglionic ceüs. rt.^,^,'^ hy.aüne continnation of the re- 



n.f. nerve fibres. tinulae. 



n.rf. nuclei of retinophorae. st. style of the retinophorae, or cr3's- 



«.//.' nucleolated nucleus of retino- talune cone cells. 



phorae. v.l. vitreous ceü layer. 



n.tf.'- aborted nucleus of retinophorae. v.b. vitreous body. 



pd. pedice!. v. crystalline cone, or vitrella. 



pg. pigment cells. 



These diagrams show, among other things, ommatidia and ocelli in various 

 stages of modification. They are drawn partly according to the observations of 

 Grenacher, Lankester, Graber and Carrière, and partly according to my 

 own. Where direct observations were wanting, the ommatidia and ocelli 

 were constructed according to deductions from my own observations. 



Fig. 128. Diagram of an omniatidium, with the corneal facet and its cells, from a 

 Compound Arthropod eye. The pedice!, walls of the retinophorae and the 

 style have been drawn in r e d for the salse of clearness, in all other cases 

 the red indicates nerve fibres ; x. is the refractive division between ad- 

 jacent facets ; a. that between the halves of each facet ; «/. thickening of 

 abaxial wall of calyx, often, butnotalways, present; the crystalline cone 

 may be present or absent, but it can never fuse with the facet, as is sup- 

 posed to be the case in Lampyris. 



Fig. 12Sa and 128b are cross sections through the calyx and middle of the style, 

 respectively. 



JFig. 129. An ommatidium from a compound eye, constructed according to Grena- 

 cher's Statements; he does not recognize the corneal hypodermis, and sep- 

 arates the eye into two layers at i?n.'; the dotted line, y., sliows tlie 

 Position of the crystalline cone when it appears to be absent. 129a is a 

 cross section of the retinulae, showing the seven (or four) rods which 

 they are supposed to scerete. 



Fig. 130. One of the isolated ommatidia from the general hypodermis of a Moüusc. 



Fig. 131. Two ommatidia from a vertebrate retina (without the outer ganglionic 

 layers). 131a, is a cross section of the rods. 



Fig. 132. Ommatidium from a Moüuscan retineura. 



Fig. 133. Ommatidium from the compound eye of ylrca or Peci^<»cM/^<s; the retinulae 

 pg.^ — 2 have lost their rods, aa is the case in all the succeeding diagrams, 

 and serve only to protect the rod of the retinophorae or become trans- 

 formed into ganglionic cells. 



Fig. 134. Ommatidium, with .an overlying portion of the vitreous layer, corneal 

 hypodermis and corneal lens, from a larvai insect ocellus. 



50* 



