Iv CONNECTING LINKS 49 
from slightly over 100° F.to112°. This highest figure 
is attained by some Passerine birds : Hawks and their 
allies are never much above 109°, and Gulls rise only a 
little above 104°. Whether these recorded temperatures 
are in every case quite exact may be doubted. When 
the subject is a wild animal, the use of a clinical 
thermometer is difficult. In the case of the python the 
results are quite dependable, though the thermometer, 
laid between the folds, no doubt registered a lower 
temperature than it would have in the mouth. With 
other animals fresh experiments are needed. But 
even as it is we may be quite certain that the figures 
given are nearly right, though there may be an error 
of a half or even a whole degree. The conclusions 
we arrive at, then, are—(1) that there is no hard and 
fast line to be drawn between warm and cold-blooded 
animals, and, consequently, our warm-blooded birds 
may be related to our cold-blooded reptiles; (2) that’ 
pterodactyls, in respect of their temperature, were 
birdlike rather than reptilian. Before leaving this 
subject, an objection raised by Sir Richard Owen 
must be met. He maintained that pterodactyls must 
have been cold-blooded since they had no feathers to 
prevent the escape of heat from their bodies. But 
the temperature of the body has comparatively little 
to do with external coverings, and depends mainly 
upon its power of generating heat and upon the 
regulating apparatus by which it adapts itself to 
changing conditions. 
We will now go on to other points which prove the re- 
lationship of pterodactyls to birds, or prove, at any rate, 
that they have developed separately on very similar lines 
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