P.vrker. — Compound. Eyes in Crustaceans. 



PLATE II. 



Argnlus. 



(Figs. 11-17.) 



Fig. 11. A section in a plane transverse to the chief axis of the body and through 

 the right eye. Depigmented. X 140. 



" 12. A longitudinal section of an ommatidium. X 475. 



" 13. A longitudinal section of an ommatidium which had been depigmented. 

 The numbers at the left of the figure correspond to the numbers 

 of the four following figures of transverse sections, and mark the 

 levels at which the latter were made. X 475. 



" 14. A transverse section through the distal end of a cone and the surround- 

 ing pigment cells. X 475. 



'•' 15. A transverse section through the proximal portion of a group of four 

 cone cells. The intercellular membranes of the cells present four 

 thickened regions. X 475. 



" 1G. A transverse section through the rhabdome. Depigmented X 475. 



" 17. A transverse section through the retinula somewhat proximal to the 

 rhabdome. X 475. 



Pontella. 



Fig. 18. The left lateral eye seen from the left side. The section is an optical 

 one; its plane is very nearly parallel to the sagittal plane of the 

 body. Depigmented in alcohol (see p. 78). X 275. 

 " 19. A transverse section of the optic nerve from a region immediately poste- 

 rior to the retina. The sagittal plane divides the nerve into sym- 

 metrical halves ; the fibres in each half belong exclusively to the 

 lateral eye of the corresponding side. X 400. 



