78 ON THE CLASSIFICATION OP BIRDS. 
are called the external and the internal webs. To 
outward appearance the form of the laminse which com- 
pose these webs, appears to be much the same as that 
of down, which has been just described, with this differ- 
ence only, that the lamina: are stronger and elastic, and 
seem to stick together, and form a parallel series, which 
the downy laminte do not. Now, this singular adhe- 
siveness is seen by the microscope to be occasioned 
by the filaments on each side of these lamin® being 
hooked into those of the next lamina, so that one sup- 
ports the other in the same position j while their elasti- 
city makes them return to their proper place in the 
series, if by any accident they are discomposed. This 
will be sufficient to give the reader a correct idea of the 
general construction of a feather, without going into 
further details on the microscopic appearance of the 
parts. In all such feathers that part only is coloured 
which is exposed to the air. It is usual to state that 
the feathers on the body of a bird are disposed or set in 
a quincunx form, thus * . | — This, however, does not 
appear to us a correct statement of the fact, the points 
of their insertion forming, in reality, only a series of 
triangles over the whole body, thus • . • ; in other words, 
they are imbricated, the termination of one forming the 
basis, as it were, of the sides of two others. It is only 
in those birds whose feathers are remarkably rigid (like 
those of the shining crests and throats of the humming- 
birds, or Trochilidai), that this disposition can be distin- 
guished externally ; but it may be readily detected in a 
recent bird, by examining the feathers where they are 
inserted in the skin. It is an error also to assert that 
these feathers are equally spread over the whole body, 
because there are few or none on the sides of the neck, 
or upon the front of the belly — in the latter case they 
would obviously be in the way of imparting the fuU 
animal warmth of the parent to the eggs in the process 
of incubation ; and they are accordingly deficient. 
(72.) The WING feathers, and those of the tail, are 
those which we have placed in the third class of the last 
