quills strike against each other and produce, as I heard in the
presence of Mr. Bartlett, a peculiar continuous sound. We can, I think,
understand why porcupines have been provided, through the modification
of their protective spines, with this special sound-producing
instrument. They are nocturnal animals, and if they scented or heard a
prowling beast of prey, it would be a great advantage to them in the
dark to give warning to their enemy what they were, and that they were
furnished with dangerous spines. They would thus escape being attacked.
They are, as I may add, so fully conscious of the power of their
weapons, that when enraged they will charge backwards with their spines
erected, yet still inclined backwards.
Many birds during their courtship produce diversified sounds by means
of specially adapted feathers. Storks, when excited, make a loud
clattering noise with their beaks. Some snakes produce a grating or
rattling noise. Many insects stridulate by rubbing together specially
modified parts of their hard integuments. This stridulation generally
serves as a sexual charm or call; but it is likewise used to express
different emotions.[408] Every one who has attended to bees knows that
their humming changes when they are angry; and this serves as a warning
that there is danger of being stung. I have made these few remarks
because some writers have laid so much stress on the vocal and
respiratory organs as having been specially adapted for expression,
that it was advisable to show that sounds otherwise produced serve
equally well for the same purpose.
_Erection of the dermal appendages_. Hardly any expressive movement is
so general as the involuntary erection of the hairs, feathers and other
dermal appendages; for it is common throughout three of the great
vertebrate classes. These appendages are erected under the excitement
of anger or terror; more especially when these emotions are combined,
or quickly succeed each other. The action serves to make the animal
appear larger and more frightful to its enemies or rivals, and is
generally accompanied by various voluntary movements adapted for the
same purpose, and by the utterance of savage sounds. Mr. Bartlett, who
has had such wide experience with animals of all kinds, does not doubt
that this is the case; but it is a different question whether the power
of erection was primarily acquired for this special purpose.
I will first give a considerable body of facts showing how general this
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