4 PEOF. OWEN ON CEBEBBA.L HOMOLOGIES 



to the reception of their impressions, is possible in tlie group in 

 which the "brain," or sum of such centres, is not traversed by 

 the alimentary canal. 



"We are thus prepared for the conception that, as the oral 

 nerve-centres in Invertebrates are so far removed from the narial 

 nerve-centres, so the ear-organs and their centres may be corre- 

 spondingly remote from the oral ones. 



Johannes Mliller recognized a structure in the fore leg of the 

 Oryllus liieroglyphus, wbicli von Siebold detected in other Ortho- 

 ptera ; and this structure was by both regarded as the true seat 

 of the auditory sense. The vesicle, in connexion with a quasi 

 tympanic membrane closing an orifice in the fore leg, receives 

 two unusually large nerves from the foremost " thoracic gan- 

 glion," ; these nerves accompany the tracheal branch of the 

 vesicle; the lesser nerve attaches itselfto the vesicular dilatation, 

 and there expands into a flattened tract, displaying a structure 

 akin to that of the acoustic-nerve lining of the semicircular 

 canals in "Vertebrates. This interpretation is accepted by the 

 experienced anatomist of the Arthropoda, Prof. Packard, who 

 writes : — " In the green Grasshoppers, such as the Katydes and 

 their allies, whose ears are situated in their fore legs, the ' first 

 thoracic ganglion ' is a complex one" *, such " auditory nerves " 

 communicating therewith. 



Although, physiologically, the remoter neural mass may be 

 compared with the part of the epencephalon in connexion with 

 the auditory organ, it may be too much to look for consent to 

 a corresponding homology. And, if such be denied, yet the 

 retral transfer of a sense-character beyond the gustatory one to 

 the foremost or even a remoter thoracic nerve-mass may not, con- 

 sequentially, affect the grounds for homologizing both the so- 

 called "supra-" and " subcesophageal " ganglia, which are con- 

 stant in regard to their special sense-nerves, with the parts of 

 the vertebrate brain similarly distinguished by relations to nerves 

 of special sense. 



Conclusions counter to these homologies either limit the term 

 " brain " to what is called the " supraoesophageal ganglion" in 

 Invertebrates, or, more consistently, involve a negation of the 

 homology of any part of the central neural system in Inverte- 

 brates with any part of that system in Vertebrates, 



* ' Second Eeport ' &c. p. 225. 



