SEXUAL CHARACTERS IN BIRDS. 



667 



and should, therefore, present little secondary sexual differ- 

 entiation. This is shown to be the case in Table lY. In this 



Table TV. 



Notes. — Compiled from F. Finn's ' The World's Birds.' 



Sexual classification as before. 



Reference Nos. :— 1 Div. 3, 13, 17, 35 : 2 Div. 7 : 4 Div. 14 : 1 Non-div. 1, 4, 6, 8, 

 9, 18, 22, 25, 28, 29. 30, 32, 36, 40, 43, 45, 46, 48 : 2 Non-div. 3, 10, 12, 15, 

 20, 26, 27, 31, 33, 37, 39, 42. U, 50 : 3 Non-div. 11, 21, 23, 38, 47 : 4 Non- 

 div. 5, 16, 19, 24, 34, 41, 49. 



table ducks form an exception — for. though capable of diving, 

 they often present sex dimorphism. In a previous table they 

 were placed with difficulty, so that it is necessary to study them 

 in more detail (see Table V..). This table shows that the diving- 



Table Y. 



Notes. — Compiled from J. Gould's ' Birds of Europe,' vol. v. 



Swans, Geese, and Sheldrakes, presenting little or no sex difference, were omitted. 

 The following list shows the placing of the ducks in the above table : — • 

 Div. v.sl.d. Fuligula leucophthalmos, Unclina leucocephala : Div. sl.d. F. oris- 

 tata, Oidemia fusca, O. nigra : Div. d. F. ferina, F. rufina, Mergus 

 alhellus : Div^. v.d. F. marila, Clangula vtdgaris, C.Mstrionica, Sarelda 

 glacialis, M. merganser, M. serrator, M. cuciilJatvs : Non-div. v.d. 

 Mareca penelope, Spatula dypeata. Anas hosohas, Querquedula crecca, 

 Q. glocitans, Q. circia, Dafila caiidacuta, Cliaiiliodes strepera, Somateria 

 mollissima, S, svectabilis. 



habit is associated with a reduction in the amount of secondarj?- 

 sexual difference. No doubt, had a larger amount of material 

 been examined, exceptions would have been encountered ; for 

 instance, in the Spot-l:)ill {Anas ]->cecilorhyncha) the sexes are 



