74 



Zoological Society : — 



of the breast-bone decreases in depth in those species which in their 

 habits most resemble the Merganser.'^ 



In the above account there are several inaccuracies. Thus, the giz- 

 zard in many of the diving ducks, taking the weight of the bird into 

 consideration, is quite as muscular as in the freshwater ducks ; in- 

 deed the nature of their food requires this provision. I have not 

 found either the above-mentioned difference in the oesophagus or in 

 the length of the alimentary canal and appendices. The oceanic 

 ducks, moreover, take a large amount of vegetable food ; and the pro- 

 portional size of the pectoral muscles in many of them is quite as great 

 as in the freshwater ducks. The keel of the sternum, too, in some, is as 

 deep ; indeed the sterna of two of the ducks in question (the Summer 

 Duck and the Ferruginous) bear in every respect a great resemblance ; 

 but to bring this matter to a more practical bearing, let me take 

 eight ducks that I have recently dissected (four oceanic and four 

 freshwater), by way of comparison of the length of the intestinal 

 tubes. The appendices are included in the length of the canal. 



Scaup {Anas marila) 



Golden-eye {A. clangula) 



Pochard {A.ferina) 



Common Scoter {A. nigra) 



Shoveller {A. clypeata) 



Pintail {A. acuta) 



Wild Duck (y^. 5o«e^a«) 



Garganey Teal {A. querquedula) 



Weight. 



oz. 

 27 

 31 

 37 



2>H 



20 



36 



42 



13 



Length of 



alimentary 



canal. 



ft. in 



7 9 



5 8 



5 



6 



5 



5 



7 



5 



Length of 

 appen- 

 dices. 



13 



10 



4 



6 

 12 

 10 



3^ 



In twenty skeletons of different species of ducks that I have lately 

 examined, I find that all have fourteen cervical vertebrae, seven cau- 

 dal, and nine pairs of ribs, with the exception of the Summer Duck 

 {Anas sponsa) and the Anas cceruleata : these have only eight ribs ; 

 but I scarcely need say that more than one specimen must be exa- 

 mined to ascertain whether this is the normal number. 



Time will not allow me to touch upon the minor differences, ex- 

 ternal and internal, which apply more or less to all families of birds. 

 Speaking generally, the short, thick-set, rounded form of the oceanic 

 duck, its short wings and neck, shorter and flatter tarsi, lobated 

 hind toe, more elastic breast-feathers, and the greater quantity * of 

 grey down upon the skin, will serve at once to distinguish it. In- 

 ternally the form of the lower part of the air-tube in the male, the 

 wider and shorter sternum, in many instances with a less developed 

 keel, and the form of the pelvis, are for the most part sufficiently 

 characteristic ; but they are none of them, I think, as regards the 

 question at issue, of special importance. 



* The Summer Duck {A. sponsa) has as complete a covering of grey down as 

 any of the oceanic ducks that I have examined, and in this respect it differs from 

 all the British freshwater ducks that have come under my notice. 



