2O0 THE INDUSTRIES OF ANIMALS. 



develop. Detritus of every kind enters into its 

 preparation : small fragments of wood, sawdust, etc. ; 

 anything is good. These Hymenoptera possess no 

 organ specially adapted to aid them ; it is with their 

 saliva that they glue this dust together and make of 

 it a substance very suitable for its purpose. The 

 dwellings often reach considerable size, yet they are 

 always begun by a single female, who does all the 

 work without help until the moment when the first 

 eggs come out ; she is thus furnished with workers 

 capable of taking a share in her task. The Vespa 

 sylvestris builds a paper nest of this kind, hanging to 

 the branch of a tree, like a great grey sphere pro- 

 longed to a blunt neck. (Fig. 33.) The Hornet's 

 nest is similar in construction. 



Gelatine nests. — These are made by certain Swallows 

 who nest in grottoes or cliffs on the edge of the sea. 

 After having collected from the water a gelatinous 

 substance formed either of the spawn of fish or the 

 eggs of Mollusca, they carry this substance on to a 

 perpendicular wall, and apply it to form an arc of a 

 circle. This first deposit being dry, they increase it 

 by sticking on to its edge a new deposit. Gradually 

 the dwelling takes on the appearance of a cup and 

 receives the workers' eggs. (Fig. 34.) These dwellings 

 are the famous swallows' nests, so appreciated by the 

 epicures of the extreme East, which are edible in 

 the same way as, for example, caviare. 



Constructions built of earth — Solitary masons. — 

 Certain animals, whose dwelling participates in the 

 nature of a hollow cavern, make additions to it 

 which claim a place among the constructions with 

 which we are now occupied. 



The AntJiophora parietina is in this group ; it is 



