1632 THE STORY OF THE UNIVERSE 



decanter hung up with the opening below. From 

 the bottom of the decanter a strong band attaches the 

 whole to the branch of a tree. The yellow weaver 

 bird of Java, as described by Forbes, constructs very 

 similar retort-shaped nests. 



These birds have no monopoly of these careful 

 dwellings; a considerable number 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 neighboring species among whom 

 the individuals work in isolation. The construction 

 of dwellings is no exception, and the nests of the so- 

 ciable weaver birds of South Africa are the best con- 

 structed that can be found. These birds live together 

 in considerable colonies; the members of an associa- 

 tion are at least two hundred in number, and some- 

 times rise to five hundred. The city which they con- 

 struct is a marvel of industry. They first make with 

 grass a sloping roof, giving it the form of a mush- 

 room or an open umbrella, and they place it in such 

 a way that it is supported by the trunk of a tree and 

 one or two of the branches. This thatch is prepared 

 with so much care that it is absolutely impenetrable 

 to water. Beneath this protecting shelter each couple 

 constructs its private dwelling. All the individual 

 nests have their openings below, and they are so 

 closely pressed against one another that, on looking 

 at the construction from beneath, the divisions can 

 not be seen. One only perceives a surface riddled 

 with holes like a skimmer; each of these holes is the 

 door of a nest. The work may endure for several 



