that connect the Orders and Families of Birds. 493 
body, which is compressed and flattened on the sides, in conse- 
quence, as M. Cuvier has informed us, of the narrowness of their 
sternum. Were we here allowed to draw an inference from the 
analogical construction of other bodies, which move with the 
greater facility through the water in proportion as they assume 
this compressed and keel-like form, we might almost conclude 
that this structure, peculiar to the birds of the present family, 
facilitates their progress through that element *, and is intended 
to counterbalance the deficiency in the formation of the foot, 
which separates them from the truer and more perfectly formed 
Water-birds. It is certain that the greater portion of these birds 
are excellent swimmers ; and in such habits, as well as in the 
shortness of their tarsi, which is equally conducive. to their 
powers in swimming, they are found to deviate from all the 
remaining groups of the order. They thus become an aberrant 
family, and lead directly, as has been before noticed, to the suc- 
ceeding order of Nafatores. The genus Parra, Linn., distin- 
guished from Rallus, Linn. by the greater length of the toes, 
and more particularly by the length and straightness of the nails, 
is yet allied to that genus by the general structure of the bill. 
With Parra may be allied Pa/amedea, Linn., and Chauna, TIl., 
the Parra chavaria of the ** Systema Nature," both of which seem 
to approach Parra in affinity, although the latter of them is so 
imperfectly known that its situation cannot be decided with cer- 
tainty. To Rallus succeeds Crer, Bechst., which by its stronger 
and shorter bill seems to lead on to Gallinula, Briss., from which 
genus, although agreeing with it in general appearance, it is de- 
cidedly separated by its terrestrial habits. Gallinula is set apart 
from the foregoing groups by the greater length of the toes, and 
the dilatation of the upper mandible upon the forehead. This 
* Mr. Wilson, speaking of the Rallus Virginianus, mentions this character as condu- 
cive to the progress of the bird through the reedy marshes. 4m. Orn. vol. vi. p. 33. 
3s2 latter 
