132 



THE STUDY OF ANIMAL LIFE CHAP. 



nests of many birds are by far the most perfect works of 

 animal art. 



Of buildings, the martins' nests by the window, and 

 the paper houses which wasps construct, are well known ; 

 but we should not forget the architecture of the mason- 

 bees, the great towers 

 of the termites, and 

 the lodges of the 

 beavers. 



It may be well 

 to notice again ex- 

 plicitly, what has 

 been suggested in 

 another chapter, that 

 while many of the 

 shelters which ani- 

 mals make are for the 

 young rather than for 

 the adults, the line 

 of definition is not 

 strict, and some 

 which were nests to 

 begin with have ex- 

 panded into homes- 

 an instance of a kind 

 of evolution which 

 i s recognisable i n 

 many other cases. 



5. Other Instances of 

 Constructive Skill.- 

 As a familiar and at 

 the same time su- 

 preme illustration of 

 constructive skill, we may take the web-making of the 

 garden-spider (Epeira diademata). (1) The spinner first 

 forms the " foundation-lines ' which enclose the area 

 selected for the future construction. These are made par- 

 ticularly strong, for they may be used for more than one 

 web. (2) From the upper foundation-line the spider drops 

 to the lower, paying out a drag line as it sinks. This line 



FIG. 38. HOUSE-MARTIN (Chelidon urbica) 

 AT ITS NEST. 



(After Brehm.) 



