9-J. MEANS OF EXPRESSION Chap. IV. 



continuous sound. We can, I think, understand why 

 porcupines have been provided, through the modifica- 

 tion 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 thev will charge backwards with their 

 spines erected, yet still inclined backwards. 



Many birds during their courtship produce diversi- 

 fied 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 spe- 

 cially 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. 8 

 Every one who has attended to bees knows that their 

 humming chancres when thev are angrv: 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 ex- 

 pressive movement is so general as the involuntary erec- 

 tion of the hairs, feathers and other dermal appendages; 

 for it is common throughout three of the great verte- 



8 I have sriven some details on this subject in niy 

 Descent of Man,' vol. i. pp. 352, 3S4. 



