244 H. K. HARTLINE, F. RATLIFF AND W, H. MILLER 



Fig. 1. Silver-impregnated section of Limulus compound eye. At the top of the 



figure are the heavily pigmented sensory portions of the ommatidia. Bundles 



containing about a dozen nerve fibers emerge from the proximal ends of the 



ommatidia. Interconnecting branches, (B); blood vessel (6. v.). 



the fine axonal branches in such regions contain vesicular structures similar 

 to those found in synaptic regions in a wide variety of animals. These knots of 

 neuropile are therefore assumed to be synaptic regions. Figure 5 illustrates an 

 eccentric cell axon (E) and a branch from the axon extending into a region of 

 neuropile (A'^). A part of the branch and neuropile are also shown in Fig. 5 

 at high magnification. The synaptic vesicles are seen within the eccentric cell 

 branch as well as other fibers comprising the neuropile. No nerve cell-bodies 

 have been found in the plexus. 



The inhibitory interaction of the ommatidia is dependent on the integrity 

 of this plexus of interconnecting fibers. Cutting the plexus bundles around the 

 strand of nerve fibers from an ommatidium abolishes all of the inhibitory 



