Essay on the Progress of the Useful Arts. 321 



chameleon's colour changes during life, and may continue to 

 change even after death. 



Bthly^ That there exists a close analogy between the mecha- 

 nism by the help' of which the changes of colour appear to take 

 place in these reptiles, and that which determines the successive 

 appearance and disappearance of coloured spots in the mantles 

 of several of the cephalopode mollusca. 



First Essay^ preliminary to the Series of Reports on the Pro- 

 gress of the Useful Arts, ordered by the Society of Arts for 

 Scotland* 



When we contrast the conditions of man at remote periods 

 of his history, we perceive an immense disparity between his 

 attainments ; and this disparity becomes the more remarkable 

 when we consider, that of, all the species of animals \^ hich exist 

 on the surface of the earth, man alone is liable to this fluctu- 

 ation. 



Each individual animal attains the complete use of all its fa- 

 culties ; and this, even though the successive generations of the 

 tribe be separated from each other by a long lapse of time. 

 With many animals nothing in the shape of instruction is needed. 

 The insect tribes at once proceed in the course that nature has 

 designed for them. No sooner does the egg burst than the larva 

 sets itself about the business of its existence ; it swims expertly 

 through the water, and seeks out its appropriate food. Led by 

 an unerring instinct, it approaches the surface of the pool or 

 climbs the stalk of some aquatic plant, and, ere the spectator 

 has time to mai-k the change, it launches off in an untried ele- 

 ment, and is undistinguished amid the thousands that have had 

 the long experience of an hour. Some again wake to life in 

 the tough bark, and eat their vermicular way through the sap- 

 wood ; till, when the metamorphosis draws near, they seek the 

 outer rind, cut it with altered mandibles, elevate their elytra, 

 unfold from beneath them their delicate wings, and use, with 

 the utmost ease, their newly acquired powers and senses. 



Ascend, as we call it, in the scale of existence, and the ele- 



• Read before the Society, 6th September 1834. 



