170 BIRDS THROUGH AN OPERA-GLASS. 
hooked at the end for holding insects; but per- 
haps the most extreme cases of adaptation are to 
be found in those of the kingfisher, humming- 
bird, crossbill, and night-hawk. In the night- 
hawk and whippoorwill the enormous fish-trap of 
the kingfisher is exchanged for — almost no bill 
at all, merely a hook and eye for a wide gaping 
mouth. 
The night-hawk and whippoorwill are the most 
nearly related of the four birds we have from the 
order of “ goatsuckers, swifts, etc.” They are 
both brown-mottled birds, and are similar in build 
and general habit. The swifts resemble the night- 
hawks in having narrow clear cut wings, small 
bills, and big mouths, but in habit they are almost 
2 ete 
