DUCKS. 



147 



are then connected by horizontal tunnels, and finally with the common entrance. Each 

 breeding chamber is closed above with a tightly-fitting piece of sod, which can be 

 lifted up like a lid, when the nest is to be examined and plundered. Such a complex 

 burrow may contain from ten to twenty nest-chambers, but in the latter case there 

 are usually two entrances. The birds, which, on account of the protection extended to 

 them through ages, are quite tame, take very eagerly to the burrows. As soon as the 

 female has laid six eggs the egging commences, and every one above that number is 

 taken away, a single bird often laying twenty or thirty eggs in a season. The birds 

 are so tame, that, when the lid is opened, the female still sits on the nest, not walkino- 

 off into the next room until touched by the egg-gatherer's hand. When no more 

 fresh eggs are found in the nest, the down composing the latter is also collected, being 

 in quality nearly equal to eider down. 



FIG. 70. Tadorna tadorna, sheldrake. 



The coscoroba duck (Coscoroba coscoroba), is a South American form which, on 

 account of its large size, graceful neck, and w T hite color is usually referred to the swans. 

 It is a true duck, however, as proven both by external and internal characters. 



The true and typical ducks (Anatinse), the central and most numerous group of 

 the family, are conventionally divided into two smaller divisions, according to the 

 presence or absence of a membranaceous lobe to the hind toe, but while there gener- 

 ally is an easily appreciable difference between a river-duck and a sea-duck, several 

 forms are so completely intermediate that it is nearly impossible to decide to which 

 category they should be referred. As far as we know, there is no character, external 

 or internal, that will naturally divide the sub-family in two. As to the value of the 

 formation of the trachea and its labryinth, we have already spoken above. The sub- 

 family is a tolerably homogeneous one, and only few outlying forms belong to it. 



