THE EVIDENCE OF THE AUDITORY APPARATUS 375 



not closely resemble the majority of the end- organs of the flabellum, 

 yet it does resemble, on the one hand, the isolated poriferous spikes 

 found on the flabellum (Fig. 149) and, on the other, the poriferous 

 goblets found on the sense-patches of the branchial appendages of 

 Limulus (Fig. 144, A), so that a combination of these two end-organs 

 would give an appearance very closely resembling that of the pecten 

 of the scorpion. 



Finally, the special so-called ' racquet-organs ' of Galeodes, which 

 are found on the most basal segments of the last pair of prosomatic 

 appendages, ought also to be considered here. Gaubert has described 

 their structure, and shown how the nerve-trunk in the handle of the 

 racquet splits up into a great number of separate bundles, which 

 spread out fan-shaped to the free edge of the racquet ; each of these 

 separate bundles supplies a special sense-organ, which terminates 

 as a conical eminence on the floor of a deep groove, running round 

 the whole free edge of the racquet. This groove is almost converted 

 into a canal, owing to the projection of its two sides. Gaubert 

 imagines that the sense-organs are pushed forward out of the groove 

 to the exterior by the turgescence of the whole organ ; each of the 

 nerve-fibres forming a bundle is, according to Gaubert, connected 

 with a nerve-cell before it reaches its termination. 



This sketch of the special sense-organs on the appendages of 

 Limulus, of the scorpions, of Galeodes, and other arachnids, and their 

 comparison with the porous chordotonal organs of insects, affords 

 reason for the belief that we are dealing here with a common group 

 of organs, which, although their nature is not definitely known, 

 have largely been accredited with the functions of equilibration and 

 audition, a group of organs among which the origin of the auditory 

 organ of vertebrates must be sought for, upon any theory of the 

 origin of vertebrates from arthropods. 



Whenever in any animal these organs are concentrated together 

 to form a special organ, it is invariably found that the nerve going to 

 this organ is very large, out of all proportion to the size of the organ, 

 and also that the nerve possesses, close to its termination in the 

 organ, large masses of nerve-cells. Thus, although the whole hind 

 wing in the blow-fly has been reduced to the insignificant balancers 

 or ' halteres/ yet, as Lowne states, the nerves to them are the largest 

 in the body. 



The pectinal nerve in the scorpion is remarkable for its size, and 



