ANTENN.K OF LEPIDOPTERA. 15 



nerve is provided with two roots ; one, ventral, composed exclusively 

 of fibres affected by s[)ecial sensibility, arises from the olfactory lobe ; 

 the other, dorsal, which includes at once motor fibres and fibres of 

 general sensiliility, arises from the dorsal lobe of the deutocerebron. 

 Viallanes also shows the correlation between the developnient of 

 nerve centres and their peripheral organs. In Libellula, whose eyes 

 are so larac, the optical gan<ilia accpiire unusual dimensions ; on the 

 other hand, in the same insect whose antenmc are very small, the 

 olfactory lobes become almost rudimentary. The reverse conditions 

 prevail in ants. 



The most plausible argument against the view that the organs of 

 smell are in the antennae is that stated by Mr. Arkle. He writes* 

 as follows : " In animal organisms the gift of scent is exercised 

 through the respiratory process. Lepidoptera possess this faculty 

 beyond doubt, and, as the air inhaled is the carrying medium, we 

 must look to the spiracles as the organs of smell." This opinion 

 rests upon the assumption that the condition found in the liigher 

 vertebrates must also obtain in lower forms. I think this is a mis- 

 take. We, who, of all vertebrates excepting the Cetaceie, have the 

 most rudimentary olfactory lobes, can have little conception of the 

 enormous range of perception, or of the mode of action of the sense 

 of smell in the lower forms. That air is the carrying medium is 

 doubtless true. Air, however, has access to the rods in the j)its of 

 the antenna?. The real question at issue, then, is whether a current 

 of air such as would be produced by respiration is necessary, or 

 whether the simple diffusion of the substance in the air would not 

 reach the organs in the antennie. That the latter condition is suffi- 

 cient is evident when one considers the state of affairs in the lower 

 vertebrates. Sharks have a highly developed sense of smell. Their 

 olfactory nerves are of great size. Yet, there is probably little or 

 no current of water over the olfactory membranes. In Amia calva, 

 a Ganoid with large olfactory nerves, the nasal sac is not connected 

 with the respiratory organs, the only communication with the outside 

 Ixjing through a narrow tube opening at its free end above the sur- 

 face of the head, and a small postnares. A number of different 

 forms do not even have a })ostnares, e. g., Petromyzoii marixn.-i. This 

 must mean that a current of the carrying medium is not a necessary 

 factor. The fact that the most careful preparations by skillful his- 



■'■• "The Entomologist." London, vol. xxvii, December, 1894, pp. 336-338. See 

 also article by Watson in vol. xxviii, February, 1895, pp. 30-33. 



TRANS. AM. ENT. SOC. XXIII. JANUARY, 1896. 



