Eyes of Mollusca and Arthropods. 



751 



Fig. 69. Onter end of an ommatidium of Penaens ; x., is a pcculiar shaped accu- 

 mulation of thickened cell substauce in which are imbedded the nuclei of 

 the retinophorae; y. clear, refractive bodies often found in the outer row 

 of pigment cells. 



Fig. Tt). A piece of the style of the retinophorae, containing the axial nerve fibre 

 iPeiiaeus). 



Fig. Tl. The same with the external fibres. 



Fig. 72. Longitudinal soction through the pedicel of the retinophorae , showing 

 the alternatiug plates with the fibres at right anglea to each other; the 

 pedicel rests upon the basal membrane by a delicate stalk which divides 

 into four legs, representing the inner ends of the retinophorae. Onl}^ the 

 scalloped and median retinula, 1, is represented [Penaeus). 



Fig. 73. Two entire ommatidia from the eye of Penaeus , showing the proportion 

 of the different parts ; especially the small size of the pedicel and enor- 

 mous dimensions of the crystalline cone. At x. is a zone of coagulated 

 semi-fluid substance. 



Fig. 74. The inner end of a pedicel showing, in a semi-diagrammatic wa}', the 

 positions of the seven retinulae. 



Fig. 75. Inner surface of the corneal cuticula, treated with boiling caustic potash, 

 showing the divisions between, and the markings upon, the corneal facets; 

 ?/probably representthe fibrousends of or the markings producedby, the 

 circle of cells surrounding the inner ends of the ommatidia (fig. 73 , y. \ 

 x. is a peculiar indentation always present in the centro of the facet; 

 d. is a very faint line of division always corresponding with the line of 

 division between the two corneal cells of each facet. 



Fig. 7B. Represents a portion of the inner face of the cornea to which the outer 

 ends of the ommatidial cells are attached. In the area above, I, are seen 

 the two nuclei of the corneal cells, e.h. , and the ends of the four retino- 

 phorae with their nuclei, v.rf. ; below III, 0UI3- the two corueal cells with 



