256 MATERIAL PROGRESS 



except under the microscope, are as complicated 

 in form as that of the nautilus, and are adorned 

 with elaborate markings that must be unseen in 

 the darkness of the ocean floor. These minute 

 organisms not only decorate themselves at the 

 cost of their environment, but effect marvellous 

 changes in it : they die, but their shells remain, 

 and, accumulated in the course of ages, form 

 deposits of immense thickness which, subse- 

 quently raised above sea-level, contribute largely 

 to the dry crust of the earth. The chalk of the 

 English downs is constituted in the main of these 

 tiny shell-cases. Corals support themselves upon 

 a stony framework which they build up from 

 materials that are dissolved in the sea: their 

 labours also have the effect of extending the earth's 

 land surface. Higher up the scale, the compli- 

 cated nests of insects and birds illustrate very 

 strikingly the action of a constructive instinct. To 

 these activities the reproductive impulse contri- 

 butes ; their architectural skill is directed to the 

 needs of their young. But there are cases, such as 

 that of the bower-bird, in which materials are 

 gathered and fashioned from the pure love of 

 fashioning, from an impulse akin to that which 

 prompts man to lay out a pleasure garden. 

 Amongst mammals the provident instinct is 

 singularly ineffective until we reach man. In 

 him it is very strongly developed, and is one 

 of the peculiarities which has enabled him so 

 greatly to outstrip all other animals. In its 

 simplest form it is the impulse to appropriate 

 that is illustrated by the thievish propensities 

 of a magpie. But when strengthened by a 

 desire for comfort, or the thousand other am- 

 bitions of humanity, it will not only compel 

 man to labour industriously ; it is a powerful 

 incentive to discovery and invention. 



