pressure of the blood be largely diminished, as would happen by having 
some of the blood withdrawn from the middle, the outside sheath of the 
feather will naturally tend to shrink. or partly collapse, in order to 
accommodate itself to the diminished turgidity ; and the manner in which 
this shrinkage takes place is the all important matter. Jt is found that 
the feather-sheath always gives way at the weaker night rings, and in such 
a@ manner as to produce a narrow wrinkle, and the wrinkling naturally 
presses upon the soft growing plume below it and thereby interferes with 
ats proper growth. The blood-pressure within the growing feather has been 
diminished , and the wrinkling of the feather represents the mechanical 
effort of the more resistant outer part to adapt itself thereto. 
The wrinkling must necessarily occur before the feather has become 
hard and firm, that is, in the early stage of its erowth, while still soft 
and unformed. Several wrinklings are often seen when a barring feather 
is drawn green from its socket, the upper ones being more strongly indent- 
FG re 
Model to illustrate how the feather becomes notched and indented at places corre- 
sponding with the weaker night growths when the internal blood pressure is reduced. The 
wall of the tube is made up of alternating stronger and weaker rings corresponding with 
the day and night growth. In the upper figure the internal and external pressures are the 
same, and tube remains smooth; in the lower figure the weaker parts of the tube have 
sunken in due to the diminished internal pressure produced by drawing out the piston. 
ed than the lower. It is thus of some importance to find that the 
shrinkage bar commences at a very early stage within the socket, in fact 
as soon as the feather-sheath has become hornified, but while soft and 
plastic. 
The wrinkling process may be illustrated as follows: a rubber tube 
closed at one end and fitted with a piston at the other is filled with water 
under ordinary pressure; if then the internal pressure is reduced, by 
drawing out the piston, the tube will partly collapse at the least resistant 
nlace, due to the outside pressure of the atmosphere upon the plastic 
rubber. The illustration more closely resembles what takes place in the 
feather if we suppose the rubber tube to be made up of alternate stronger 
and weaker rings. While under ordinary pressure the surface of the tube 
will be smooth, as in the upper diagram in fig. 7, but on reducing the 
internal pressure, by drawing out the piston, the tube will tend to 
collapse and wrinkle at the thinner, weaker rings, as shown in the lower 
diagram. And this is what happens in the growing feather, where the 
stronger and weaker rings correspond with the day and might growth. 
We must look upon the growing feather as a long narrow tube, closed 
above and open to the blood supply below; also the tube is made up of 
alternate stronger and weaker rings, and is filled internally with the blood 
fluid under a certain pressure. The upper part of the tube where the 
