GUSTATORY ORGANS. FLABELLUM. 



"3' 



If the mandibles on one side are stimulated, the cheUcera of that side, al- 

 though not stimulated itself, extends rigidly backward, or waves aimlessly back 

 and forth snapping its chelae and thrusting the tip of the appendage into the mouth. 

 If the jaws on the opposite side are now stimulated, the chelicera on that side 

 begins to work also. 



The chewing reactions can only be produced by stimulating the spines on 

 the mandibles, or the smooth, under surface of the inner mandibular spur. Stimu- 

 lating the skin around the mouth, or in it, does not produce the chewing reflexes. 

 If the mandibles are amputated, no reaction in 

 the leg so treated occurs. If the spines are shaved 

 off, the reaction is produced only after strong stimu- 

 lation, or by stimulating the under surface of the 

 inner mandible. 



It is thus evident that we are dealing with true 

 taste organs, and that they must be located in the 

 mandibular spines. 



b. Structure of the Gustatory Organs. — The 

 mandibular spines are thickly covered with minute 

 pores arranged in vertical lines. (Fig. 83, A.) The 

 pores lead into canals, each of which contains a 

 long, slender chitenous tubule that terminates flush 

 with the outer surface. The chitenous tubule 

 contains an exceedingly fine, hair-like prolongation 

 of a gustatory cell. Toward its inner end, the 

 tubule expands into a peculiar spindle, beyond 

 which lies the nucleated cell body. The gustatory 

 cells are united into spindle-shaped clusters, each 

 cluster corresponding to a single line of pores. 

 The central ends of the cells are continued as nerve 

 fibers into the main gustatory nerve, which extends 

 over the surface of the pedal ganglia, through the 

 gustatory tracts, to the common centers in the 

 chehceral lobes and hemispheres. (Figs. 65-114.) 



Fig. 83. — .(4 , Gustatory coxal spine 

 of Limulus, showing linear arrangement 

 of the gustatory pores; B, longitudinal 

 section of a gustatory spine, showing 

 the gustatory cells, g.s.c,, spindles, sp^ 

 and chitenous end tubes, sch.t. highly 

 magnified. CD, Details of surface 

 terminals. 



The flabellum is a large spatulate organ, one 

 to one and one-half inches long, attached to the outer side of the coxal joint 

 of the sixth leg. It lies in a channel leading into the respiratory chamber, so 

 that the water going to the gills passes over its flat anterior surface. The latter 

 is perforated with innumerable canals that afford an opening for the elements 

 of the underlying sense organ, the most voluminous one in the whole body. 



Each canal contains the outer end of a pear-shaped sense bud composed 

 of eight to twelve, or more, sense cells. The buds are loosely united into small 



