80 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
to which the domestic Duck is now reduced might quite 
possibly have been in operation sufficiently long (though 
for how long we have no definite data) to have resulted in 
some reduction of the keel of the sternum as compared 
with that of the wild bird. I therefore obtained specimens 
of the sterna of Anas boschas, and of the domesticated 
species, and from these specimens, which I show you, 
both taken, I may say, from adult, full-sized birds, it 
seems clear that a reduction in the carina sterni of the 
domesticated bird is in course of progress. As domesti- 
cated Ducks vary not a little in bulk, the size of the 
sternum, as of other parts of the skeleton, will be liable to 
corresponding variations, and a considerably larger number 
of measurements than I have been able to make would be 
desirable, but the specimens before you probably represent 
a fair average. The sternum of the domestic Duck is, of 
course, larger than that of the wild bird, in harmony with 
the larger size of the bird itself, the specimen I have 
chosen measuring 10 cm. in length and 5:2 cm. in breadth, 
as compared with a length of 9°2 cm. and a breadth of 4°8 
cm. in the specimen of the sternum of the wild bird. 
Other things being equal, we might expect a deeper keel 
to go with the larger sternum; but, as a matter of fact, I 
find that the reverse is the case. The carina sterni of the 
domestic bird is not only of less depth than that of the 
wild bird, but its shape is different, for, instead of describ- 
ing a definite convex curve from its anterior to its posterior 
extremity, as that of the wild bird does, it runs from 
before backward as a nearly straight ridge, the curve it 
does describe being very slight, diminishing in depth, of 
course, as it proceeds backwards. At the extreme anterior 
ends the sternal keels of the two birds are alike in depth, 
measuring 2°5 cm. each, but from this point backwards 
the keel of the wild bird is everywhere deeper than that of 
