OLFACTORY ORGANS OF LIMULUS. 



161 



far as I have been able to discover without a thorough application of either the 

 methylene blue or the Golgi method, there are three ways in which the nerves 

 may terminate in the region of the olfactory organ. The median nerve, be- 

 fore reaching the organ, breaks up into numerous small branches which are 

 distributed in the central portion of the organ. (Fig. 109, m.ol.n.) The two 

 lateral nerves terminate in oblong masses of very large ganglion cells, just be- 

 neath the lateral margin of the organ. From these ganglia numerous branches 

 arise that are distributed to the olfactory organ and to a considerable area of the 

 surrounding epidermis. 



The finer branches from both sources form a sub-epithelial plexus, from which 

 still smaller branches are distributed over the surface of the slime buds. Others, 



orr 



FIG. 109. The olfactory organ of Limulus. .4, Olfactory organ of the adult, seen from the outer surface; 



B, cross-section through the olfactory organ of a young Limulus, about seven inches long (Flemming's solution) ; 



C, longitudinal section through the root of the lateral olfactory nerve of a young Limulus, showing the ommatidia- 

 like clusters of large cells with rod-like enclosures, derived from the primitive segmental sense organs. 



possibly derived exclusively from the lateral olfactory nerves, end in peculiar 

 ill defined masses of cells that are either wedged in between the slime buds, or lie 

 against the epidermis. (Fig. 88.) They may possibly be connected with slender 

 sensory cells, similar to those in the gustatory organs, that extend into the 

 hollow spines and into the narrow canals leading to the outer surface. 



Finally there appears to be a system of fine nerve strands that penetrate 

 the soft chitenous exoskeleton surrounding the olfactory organ, where they form 

 loose meshworks in superimposed layers. These fibers resemble those seen in 

 the cornea of mammals, and although of very uniform caliber they appear to dif- 

 fer from the branching hyphse of the parasitic fungus (Macrocystis) that is fre- 

 quently seen in this region. The hyphas take up the methylene blue in a similar 

 manner to nerve fibers, and at first sight might be easily mistaken for them. 

 However, recent preparations in von Rath's fluid show, in addition to the hy- 

 phas above mentioned, branching fibers that appear to be true nerve-fibers. 



ii 



