THE CEMENT OF BIRD MASONS 177 



tures along the edges of the leaf to be utilised, it pro- 

 cures some cobweb, and, having attached it to one edge 

 of the leaf, carries the strand across to the other edge 

 and, before attaching it to this, pulls it so tightly as 

 to draw the two edges together. When the nest has 

 taken its final shape the bird strengthens the first 

 attenuated strands of cobweb b}^ adding more cobweb 

 or some threads of cotton. 



Many birds which weave their nests plaster the 

 exterior more or less thickly with cobweb so as to add 

 strength to the structure. 



It would be wearisome to detail all the kinds of nest 

 into the composition of which cobweb enters. Suffi- 

 cient has been said to show that this very useful 

 substance is the favourite cement of bird masons. 



N 



