306 



INTRODUCTION TO ZOOLOGY. 



In the former part we mentioned (p. 137), that some Cater- 

 pillars spin a snow-white canopy, and dwell together in social 

 communities. Among birds wc have an example of their 

 united efforts being, in like manner, employed in the construc- 

 tion of a common covering. This is observable in the Sociable 

 Grosbeak (^Loxia soda), a species fomid about the Cape of 

 Good Hope. These birds construct a roof of grass matted 

 together ; and beneath the eaves of the shed thus formed by 

 their joint labour, the individual nests are built {Fig. 254). 

 Some idea of the size and solidity of these structures may be 

 formed from the fact mentioned by Vaillant,* that having 

 observed one of enormous size, he despatched some men with 

 a waggon to bring it, and on its arrival he cut it to pieces with 

 a hatchet. 



Fig. 251.— Xest of Sociable Grosbeak. 



Organs of Voice. — The period when birds are about build- 

 ing their nests, and engaged in attending to the callow young, 

 is that in which our groves become "prodigal of harmony." 

 This may, therefore, be a fitting place to make some remarks 

 on the organs of voice. In birds they consist of a wind-pipe, 

 which divides at the lower part into the two branches called 

 the bronchial tubes — one leading to each lung (as shown in 



* Travels, second series, vol. iii. 



