LTASSIC FORMATIONS. 
73 
Pterosaurs have been found associated with their tendons/ that detached caudal vertebrae 
of Archaopteryx might be recognised through the want of them. 
We may confidently conclude that the Oolitic mud which has entombed the greatest 
number and variety of the flying reptiles of its period would have shown us, when petrified 
into lithographic slate, their feathers, if, as warm-blooded animals, they had needed such 
heat-conserving a covering. The plumose clothing of the long-tailed bird of the period 
proves its haematothermal character, as the want of it shows the long-tailed pterosaur to 
have been cold-blooded. 
The tyro, fresb from the lecture-room of his physiological teacher, ambitious of soaring 
into higher regions of biology than were opened to him at the medical school, impressed 
with the relations of active locomotion to generation of animal heat, may be pardoned for 
inferring that the amount of work involved in sustaining a Pterodactyle in the air would 
make it, physiologically, highly probable that it was a hot-blooded animal. But a competent 
friend, finding him bent on rushing with such show of knowledge into print, would counsel 
him to provide himself with a thermometer adapted to the delicate testing of the internal 
heat of small animals. So provided, if he should chance to beat down a chafer in full flight, 
the experiment, made with due care and defence of the fingers guiding the instrument, 
would teach him how fallacious would be the inference that, because an animal can fly, it 
must, therefore, be hot-blooded. Unless he happen, in introducing the bulb by the 
widened vent into the abdomen, to plunge it into a mass of ova, he will find the heat of 
the beetle, notwithstanding the amount of work involved in sustaining and propelling 
itself in air, not to exceed by more than one degree that of the atmosphere. If he has 
knocked down a female cockchafer prior to oviposition, the ovarian masses may indieate half 
a degree, or even one degree, higher of temperature (Fahr.). With the cooling of the air 
in the summer night the temperature of the Melolontha concurrently falls. So, likewise, 
would that of the flying reptile, whatever “ amount of oxidation and evolution of waste 
products in the form of carbonic acid ” " might have attended their exercise of flight. The 
constant correlative structure with hot-bloodedness is a non-conducting covering of the 
body. We may with certainty infer that Archceopteryx was hot-blooded, because it had 
feathers, not because it could fly. 
There is no ground, from observation of the Sharks and Porpoises that accompany 
swift-sailing vessels, maintaining themselves near the surface, exercising their several and 
characteristic evolutions in quest or capture of prey, for inferring that the amount or the 
energy of muscular action is very different in the two surface-swimmers. 
Sharks have and, no doubt, work a greater proportion of muscle than Cetaceans ; a 
less proportion of their body is excavated into visceral cavities. Yet the Shark is cold- 
blooded ; its temperature rises and falls with that of its medium ; it has no provision, by 
1 As seen in PI. II, at cd, and in PI. Ill, figs. 3,4, 5. 
2 ‘Proceedings of the Zoological Society,’ April, 1867, p. 417, Prof. Huxley “On the Classification 
of Birds.” 
10 
