PROFIT AND LOSS IN THE BIRDS. 193 
useless by change of habit. But some of them per- 
sist yet as vestiges of past conditions. When birds 
took to water they developed webs between the toes, 
and their toe tendons split up and spread out to each 
digit, in keeping with very complicated needs. Ves- 
tiges of these persist (in the fowls, birds of prey, 
and others) with peculiar arrangements of tendons to 
pull the outer toes in under the middle, as if to offer 
little resistance to the water on the forward swimming 
stroke. Many of the lower birds that are not swim- 
mers retain a muscle whose sole use was to close the 
front toes automatically when the leg is bent. 

Head of gannet (1) and cormorant (2) showing abortive nostrils. 
Some of the diving birds have lost their nostrils, 
and others which gulp their food, judging of its fit- 
ness by sight only, have lost their tongues. An un- 
used organ always tends to go, at least till it gets out 
of the way. Internally also have. come about great 
changes and losses. | 
