THE SPIDER 



103 



the purpose of protecting the young or forming a communal 

 home than for the purpose of entrapping prey. The forms of 

 webs invented by spiders are very numerous and their study 

 is full of interest. We shall consider them further on, after we 

 have learned something of their structure (Fig. 105). 



In the vertebrates the simplest homes are those made by 



Fig. 105. — Web of Tctragnatha, placed horizontally over a fish-way. Photo, 

 by W. H. C. P. 



fishes. These may be merely piles of pebbles to cover the eggs 

 or they may rise to the complexity of nests woven of plant 

 fibre, as in the case of the sticklebacks (Fig. 315). The comph- 

 cated nests built by birds, for the purpose of rearing their 

 young, reach their highest expression in our Baltimore 

 oriole and in the tailor bird of Australia. Finally among 

 the mammals we find examples of animals that burrow 

 like the wood rat of the Great Basin; that build houses 



