A History 
of Birds. 
(73) 
THE BIRD WORLD. 
Photo copyright by] [ W. S. Berridge, F.Z.S 
White Penguin, “ eye-and-wing marked." 
In Penguins the wing is well-developed, but does not fold, 
and is only used as a swimming-paddle. 
the smaller perching birds, such as Finches; 
Hawks do not maintain a temperature above 109 
deg., and Gulls only a little above 104 deg. 
This rise in the temperature of the blood 
which, as we have said, we meet with first in 
the birds, is due to several causes which are too 
technical to be discussed here in detail. But 
chiefest among them we may count the fact that 
the heart of the bird, like that of the mammal, 
is a four-chambered heart, whereby a more per¬ 
fect oxidation of the blood is possible than is the 
case with the reptiles, which have but three 
chambers. That is to say, the impure blood 
brought back to the heart is, when passed 
through a four-chambered heart, thoroughly 
purified by the air drawn in by the lungs, and is 
sent back over the body without mingling with 
the returning impure blood. In the reptile this 
mingling is unavoidable, and consequently a 
smaller quantity of the heat-giving oxygen is 
brought into the system. But, strangely enough, 
the blood of the reptiles and birds agrees in this, 
that the little red bodies, or “ corpuscles,” whose 
duty it is to absorb the air from the lungs and 
the carbonic acid from the tissues of the body, 
have each a central “kernel” or “nucleus,” 
whereas the blood corpuscle of the mammal has 
no nucleus. 
It would be wearisome to expand further this 
question of the temperature of the blood, since 
to thoroughly understand this matter a some¬ 
what intimate knowledge of physiology and 
'chemistry is required. It is, in short, a question 
for the physiologist and the medical man, rather 
than for the ornithologist. 
It may seem that this answer to our question, 
“ What is a bird? ” has taken us rather far afield. 
And in this account it may be well briefly to sum¬ 
marise the facts which have been gleaned on the 
journey. 
Bird Characteristics Summarised. 
In a fe\v words then, a bird is a warm-blooded, 
egg-laying, feathered biped, having the fore-limbs 
modified td form wings, and the hip-girdle sb 
adapted as to bring the hind-limbs far forward, 
to balance the body in walking. These charac¬ 
ters, there can be no reasonable doubt, have 
gradually cOme into being by the slow transfor¬ 
mation of a long chain of creatures which, as 
we trace them back, grow less and less bird¬ 
like, and more’ and more like reptiles. Though 
many links in this chain are yet missing, some 
day they will almost surely be found. 
The evidence for this reptilian descent is abun¬ 
dant. Every bird, in the course of its growth 
from the egg- onwards, passes through more 
or fewer of the ancestral stages, and while some 
of these carry us back to phases of development 
which belong to ancient types of birds long since 
extinct, others carry us yet farther, and show, 
in a way that makes contradiction mere stupidity, 
that the birds and the reptiles have descended 
from the same common stock. 
Those who are not naturalists, who have had 
no practical experience in the breeding and mating- 
of animals, often fail to see the force of this 
evidence. It is otherwise, however, with those 
who have traced out for themselves the intricate 
pi oblems of pedigrees, for the nature of the evi¬ 
dence and the line of reasoning which apply in 
tracing descent back a few generations, apply 
also in tracing back a thousand, or ten thou¬ 
sand. 
(To be continued’.) 
Photo copyright by] [Lewis Medtand, F.Z.S. 
Secretary-bird ^killing a Snake. 
