172 THE OLFACTORY ORGANS AND THE OLFACTORY LOBES. 



In order to test its glandular nature, the olfactory organ was cut out, its outer 

 surface wiped dry, and then the attached nerves stimulated with electricity; 

 no traces of a secretion appeared. But electrical stimulation of the olfactory- 

 region in uninjured male crabs in some instances at once produced very remark- 

 able leg movements, rarely seen under any other circumstances. 



When the electrodes are applied to the olfactory organs of the male, if the 

 experiment is successful, rapid chewing movements of the mandibles are produced, 

 accompanied by vigorous snapping of the chelicerae, which may finally become 

 rigid and stretched out backward at full length. At the same time the second 

 pair of legs (the ones used to seize the females) which during all our preceding 

 experiments on the gustatory organs have remained motionless, are now quickly 

 and repeatedly flexed, as though trying to hug or grasp some object and force it 

 toward the mouth ; all the other legs remain motionless. Stimulation of the region 

 about the olfactory organ, or along the median line between the olfactory organ 

 and the brain, or above the brain, may produce the same effect. 



These experiments indicate that the olfactory organ is a chemotactic organ, 

 whose activities are associated with the process of eating, although it is difficult to 

 explain why the chewing movements are not produced by direct stimulation of the 

 olfactory organ with food. On the other hand, the extraordinary hugging and 

 grasping movements aroused in the second pair of legs of the males, when the 

 organ is electrically stimulated, indicate that it is used in finding the females during 

 the mating season. That an organ for this purpose must be present seems cer- 

 tain, for the males during the breeding season seek out the females and attach 

 themselves to them with great precision. In confinement, the males usually 

 attach themselves to the abdomen of the females, but males whose olfactory 

 organ had been cut out did not do so. Smearing the olfactory organs of males 

 with the ova or secretions of oviducts produces no effect. 



In primitive vertebrates, the olfactory organ was doubtless of great importance 

 in mating, as indeed it is through the whole series of vertebrates. It is of special 

 interest that they were intimately associated with sexual activities in such remote 

 ancestors of the vertebrates as the arachnids. In this connection, the olfactory 

 function of the antennae of insects, and its relation to sexual reproduction will be 

 recalled. 



Summary and Conclusion. 



The gustatory organs play an important part throughout the entire range of 

 arthropods, and they have done so ever since the appendages have been used as 

 aids to nutrition. In Limulus, they form the most voluminous nerve tracts and 

 nerve centers of any single set of organs, and the great size of the hemispheres is 

 largely due to important gustatory centers that are located in them. 



The olfactory apparatus and the olfactory function arose in the higher 

 arachnids through the secondary modifications of preexisting organs that had 

 some other function or meaning. 



