THE UNGUIROSTRES. 147 



inferior tract are generally very broad, rounded, particularly strongly curved, and elastic. By this 

 means they lie very close together, and completely repel the water during natation. The oil- 

 gland, which, by its secretion, promotes this property of the contour-feathers, is of a cordate form 

 and of considerable size. Each half contains only one cavity, and opens by a separate orifice on 

 the pointed mamilla, which is crowned by a circlet of oil-feathers. The powerful remiges vary in 

 number from twenty-four to thirty-four, but there are always ten on the pinion, and the first of 

 these is generally the longest, more rarely the second, and very seldom (in Anas moscJiata} the 

 fourth. The rectrices are remarkably soft, small, and very variable in number, ranging between- 

 twelve and twenty-four. 



Of the five genera of this family there is only one Cereopsis, 1 that I have been unable to 

 examine ; of the other four the following were accessible to me : 



1. Cygnus. Contour-feather-tracts exactly as in Anser cinereus ; the spinal space, also, is of 

 the same length, at least in C. olor and musicus, which I examined. Both species have more than 

 thirty remiges, the second certainly thirty-four, of which ten are'seated on the pinion ; the second 

 is the longest. The first three have a strong angular emargination on the inside of the vane. In 

 the tail I found twenty-four feathers in C. musicus, in C. olor only twenty-one, and on one 

 occasion only sixteen. The large oil-gland has long and strong oil- feathers and two wide orifices 

 (see p. 41). 



2. Anas. This genus is distinguished by the longer and stronger terminal branch of the 

 inferior tract, and has a still shorter lateral neck-space than the rest. Notwithstanding a great 

 general similarity, two pterylographic groiips may. be established in it, and these differ also 

 zoologically from each other in the form of the hinder toe. 



a. The Pochards (Hydrobates, TEMM.) have a shorter spinal space, which is generally 

 limited to the interscapulium (as in Dysporus, PI. X, fig. 9), and never extends beyond the com- 

 mencement of the pelvis. In other respects they are distinguished by a still denser plumage, 

 and by the presence of the aftershaft, which, indeed, is often very small, for example, in 

 A.fuligula. I have seen it more distinctly in A. lobata, TEMM., and A. clatiffula, in which it is of 

 considerable dimensions. Most of the species, such as A. lobata, fuligula, ferina, leucopldlialma, 

 ri/fina, mollissima, marila, nigra, clangvla, and glacialis, have twenty-six or rarely twenty-seven 

 remiges, of which ten are seated on the pinion, and fourteen rectrices ; but of the latter A. lobata, 

 possesses twenty, A. leucophthalma eighteen, A. rufina and nigra sixteen, and exceptionally 

 A. clangula has seventeen and A. leucopldlialma fifteen. 



b. In the true Ducks the spinal space generally reaches from the base of the neck to the 

 caudal pit (PL X, fig. 6), and is somewhat shorter only in particular species, for example, in 

 A. tadorna and crecca. I have never observed an aftershaft in them. In the wings I have 

 usually counted twenty-six remiges, of which the second is generally the longest ; in A. moscJiata 

 alone the fourth was the longest, and the preceding three were graduated. A. tadorna has 

 thirty remiges, and A. crecca only twenty-four. In the tail I found fourteen feathers in 

 A. penelope, tadorna, boschas, querqnedula, and clypcata ; sixteen in A. crecca and acuta ; but 

 the curled feathers of the male individuals are true tail-feathers, and not tail-coverts, and these 

 raise the number to twenty, at least in A. boschas. The females have the same number. 



3. Anser. The spinal space extends to the commencement of the pelvis, and the lateral 



1 I have only ascertained the number of tail-feathers in this bird, which is sixteen. 



