VI FORM AND FUNCTION 67 
work, the process of digestion is complete, and the 
food goes to build up the living animal. The wonder- 
ful process mentioned above is in full swing here; 
the chyle, that part of the food which consists of 
emulsified fats, passes into the lacteals (to be described 
later on) through the villi, small creases in the coat of 
the intestine, the rest into the blood-vessels, and so, in 
either case, on to the heart. All refuse is carried into 
the large intestine, any return from which is prevented 
by a valve. 
Before leaving the subject of digestion, I wish 
to show how important an organ the liver is to birds. 
For purposes of flight their weight is reduced as much 
as possible, but in some good flyers the liver is ex- 
traordinarily heavy. In the Tern it is py of that of 
the whole bird, in the Swallow #,, in Vanellus 
Cristatus, a kind of Lapwing, 7, in the Smew yy. In 
all these it forms a far larger fraction of the whole 
than in man. And how account for the great differ- 
ences? The Smew is mainly a fish-eater and also the 
Tern. But in the fish-eating Heron the liver is said 
to be remarkably small. In the common Fowl it 
contributes rather less than »; of the total weight, 
suggesting that seed-eaters depend comparatively 
little on the liver and more upon the gizzard. But 
in corn-eating pigeons we find both large gizzards and 
large livers. And the liver of the flesh-eating gizzard- 
less Kestrel is lighter than that of the Fowl, only 3g, in 
fact, of his total weight, while in the Tawny Owl it is 
less than.j,. These facts are very perplexing. Dr. 
.Gadow in quoting them remarks that they are un- 
trustworthy, since they must be affected by the con- 
F 2 
