190 



THE INDUSTRIES OF ANIMALS. 



dwellings ; a considerable nunnber of genera have 

 carried this industry to the same degree of perfection. 

 When animals apply themselves in association to 

 any work, they nearly always exhibit in it a marked 

 superiority over neighbouring species among whom 

 the individuals work in isolation. The construction of 



Fig. 28. 



dwellings is no exception, and the nests of the Sociable 

 Weaver Birds of South Africa are the best constructed 

 that can be found. These birds live together in con- 

 siderable colonies; the members of an association are 

 at least two hundred in number, and sometimes rise 

 to five hundred. The city which they construct is a 



