W. H. FURLONGE ON THE PULEX IRRITANS. 191 



starting from the upper anterior portion of the margin of the 

 cavity, curves, downwards and backwards, to the lower edge of its 

 base, a little behind the eye, which is entirely surrounded by this 

 projecting plate. 



The Antenna. — Within the chamber thus formed, is situated a 

 highly curious organ, of complex structure, apparently composed of 

 a somewhat soft substance of a yellowish-white colour. Its form 

 resembles that of a curved pear, the smaller extremity being turned 

 upwards and backwards, and aj^pears to form the orifice of a tube 

 curving backwards, and expanding into the posterior bulbous extre- 

 mity of the organ, the upper edge of which is apparently pectinate, 

 owing to the bulb being transversely cleft, for about half its thick- 

 ness, into laminas. The entire organ is attached to the anterior 

 portion of the cavity, by a short muscular foot-stalk or peduncle, by 

 means of which it can be thrust out, almost at a right angle, hori- 

 zontally, over the edge of the cavity, at the will of the animal. A 

 remarkable row of very long, stiff setaa, of a whitish colour, and 

 about 10 in number, spring from the curved anterior portion of the 

 organ, projecting backwards and lying in a nearly horizontal posi- 

 tion above it, for the whole length of the cavity. The fringe, or 

 brush, thus formed, may, perhaps, simply serve to protect the delicate 

 structure beneath from particles of extraneous matter, but it is, in 

 my opinion, more probable that they are sensorial hairs, or seta?, 

 which convey impressions to the brain, or nervous ganglia, lying 

 behind the base of the peduncle. 



For the more complete protection of this obviously very delicate 

 organ, a long triangular flap, or valve, of extremely thin mem- 

 brane, is attached to the edge of the lower portion of the fixed 

 chitinous plate previously described, and of which it, in fact, forms, 

 a continuation, when the organ is at rest, so as to cover over about 

 two-thirds of the opening of the chamber, but when the organ is 

 protruded the valvular flap is pushed down, returning to its erect 

 position when the organ is retracted. 



The curious pair of organs just described, have generally, and 

 no doubt properly, been regarded as the antennas of the insect, 

 but, after much observation, I cannot resist expressing the conjec- 

 ture that they may probably — specifically, if not solely — serve the 

 purpose of hearing organs, my reason for this suggestion being as 

 follows : — From their position, the organs in question are capable 

 of only very limited movement, and from their peculiar structure, 



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