470 
On the Tail-feathers of the Dabchick. 
some of the apparent coverts are not in reality degenerate 
rectrices ; but on the whole it does not appear that more than 
eight can be regarded as answering to rectrices. These, 
with their coverts, are arranged in a double series, one on 
either side of the middle line and running parallel with one 
another, leaving a well-marked apterion between them. 
The slight concavity which these two rows euclosed in the 
specimen originally examined—which caused me to describe 
them as arranged in the form of a horseshoe—was, 
I find, an individual peculiarity. As a matter of fact, the 
two rows—eliminating the coverts—run parallel one to the 
Text-fig. 10. 
Tail-feathers of Poclicipes Jluviatilis. 
A. Section through the tail, exposing the caudal vertebrae, to shew the 
relation of the rectrices to the pygostyle. 
B. Superficial appearance of the bases of the rectrices. 
C.V. = Caudal vertebrae. P. = Pygostyle. 
0. = Oil-gland. R. = Rectrices. 
other, and, be it noted, have their ventral aspects turned 
towards each other, as in many Gallinaceous birds. 
This peculiar arrangement would seem to have come about 
as a consequence of the degeneration of the caudal vertebrae, 
and the shortening of this region of the vertebral column 
attendant thereon : the rectrices having been thus slowly 
