14 
which we are familiar are probably subject to just as many vicissitudes 
as is the ostrich, and yet faulty feathers are the exception among them, 
whereas among ostriches their presence is the rule. Even when the ut- 
most care is given to the birds by farmers with years of experience, and 
with all the best farming conditions available, the feathers are still more 
or less defective, while under adverse conditions they may be nearly 
worthless. It can safely be asserted that ostriches under ordinary farm- 
ing conditions, even where kept in a good state of health, are incapable 
of producing a plumage entirely free from bar faults, and such would also 
appear to be the case with the wild bird, so that the trouble cannot be 
put down to domestication alone. Tt 7s a remarkable biological fact to 
find that an animal is incapable, even under highly nourished condi- 
tions, of producing an important part of its structure im a wholly per- 
fect manner. Regarded from an evolutionary point of view we may sur- 
mise that the feathers of the ostrich, being of no use as organs of flight, 
are retrograding, that is, it has become of greater advantage for the 
bird that the nutritive forces should be turned in other directions; and, 
therefore, we get the very delicate balance of feather nutrition, to be dis- 
turbed by the shghtest adverse conditions. 
IT am inclined to consider that climatic changes also have a greater 
influence upon the ostrich than upon other birds. Its plumage is appa- 
rently not well adapted for protecting the body from the great extremes 
of temperature to which it is subject. Considering the readiness with 
which the bird erects its feathers on warm days, it would seem that they 
are not very effectual as a protection against the sun’s heat, and we may 
assume that the plumage is just as ineffectual in the retention of the body- 
heat during cold weather. Owing to the absence of hooklets on the bar- 
bules, the flue of the ostrich, like that of other running birds, is loose in 
character compared with the compact vane of flying birds; and it can 
hardly be considered that a loose plumage will serve to protect the body 
from temperature changes so effectively as an almost air-tight covering. 
It is significant in this connection that the Rhea referred to above as 
having an intensely barred plumage belongs, like the ostrich, to the flight- 
less birds with loose flue to the feathers. The practical absence of down 
feathers and filo-plumes in the ostrich, compared with other birds, also 
needs to be taken into account. The smaller down feathers, which in 
most birds are interspersed among and below the larger contour feathers, 
form, as it were, a second plumage which serves for the better retention 
of the heat of the body; but the ostrich is without this additional protec- 
tion, having only its single covering of contour feathers. Further, the 
ostrich hag extensive naked areas altogether destitute of feathers, namely, 
the legs and a large space along each side of the body. Variations of tem- 
perature acting upon such an insufficiently protected skin would be ex- 
tremely likely to modify the blood-pressure, both within the greatly pro- 
truding growing feathers and the surface of the skin itself. We need 
only mention the extreme changes in temperature between the day and 
night to which South Africa is subject, and even the remarkable changes 
often from day to day, to be impressed with the influence which tem- 
perature must exert upon the ostrich. 
The great sensitiveness in the nutrition of the feather and the marked 
résponsiveness to climatic changes will go hand in. hand in producing 
those variations of blood-pressure within the growing feather which result 
in the formation of bars; either would be sufficient to produce the faults, 
but generally they will act cenjointly. 
One can readily understand that if the ostrich has this natural ten- 
dency to the production of faulty feathers, the tendency will be likely to 
be accentuated under domestication, particularly under the varying ‘and 
often uncertain farming conditions which ‘prevail in.South Africa. The 
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