150 Mr. H. G. Seeley on Prof. Owen's 
been given as evidence that heat is not dependent upon energy ; 
for here the heat is not generated but only conserved. 
In ascending from the lower to the higher groups of the 
vertebrate province, increase in temperature is found to 
sociated with perfection of the respiratory system, and not 
necessarily with a non-conducting covering ; and it is to su- 
perior respiration and its concomitant superior nutrition that 
must be attributed, as a chief cause, the grades of organization 
which divide vertebrate animals into classes. Any modifica- 
tion of the skeleton which throws light on the respiratory 
function is therefore of great classificational value in palæ- 
ontology. The avian type of skeleton differs typically from 
that of other classes in having the respiratory organs prolonged 
into the bones. It is stated by a good observer, and is, I be- 
lieve, well known, that 1f the larynx of a bird be tied, and the 
umerus broken, and the fractured surface exposed, the animal 
will breathe feebly through its humerus. Similarly to birds, 
unlike all other animals, the bones of Pterodactyles show 
pneumatie foramina, which, so far as comparable, are placed, 
as in birds, in the limb-bones and vertebral column. I draw 
the conclusion, therefore, that the foramina are evidence in 
Pterodactyles that the respiratory organs extended into the 
nes; and seeing that from a bird’s bone with this pneu- 
only known clue to their interpretation. Prof. Owen admits 
and many mammals air is admitted to several bones, but this 
see 
LB He LAL RP SEOANE ASIE] dias Ro Hcc ter UELUT SNOS 
