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The Descent of Man

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ut the chief difference is that the whole upper<br />

surface <strong>of</strong> this segment, when held in the proper<br />

light, is seen to be clothed with hairs, which<br />

are absent or are represented by excessively<br />

fine down in the males. It should be noticed<br />

that in all Coleoptera the effective part <strong>of</strong> the<br />

rasp is destitute <strong>of</strong> hairs. In O. senegalensis the<br />

difference between the sexes is more strongly<br />

marked, and this is best seen when the proper<br />

abdominal segment is cleaned and viewed as a<br />

transparent object. In the female the whole surface<br />

is covered with little separate crests, bearing<br />

spines; whilst in the male these crests in<br />

proceeding towards the apex, become more<br />

and more confluent, regular, and naked; so that<br />

three-fourths <strong>of</strong> the segment is covered with<br />

extremely fine parallel ribs, which are quite<br />

absent in the female. In the females, however,<br />

<strong>of</strong> all three species <strong>of</strong> Oryctes, a slight grating<br />

or stridulating sound is produced, when the<br />

abdomen <strong>of</strong> a s<strong>of</strong>tened specimen is pushed<br />

backwards and forwards.

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