76 
SYSTEM OF NATURE. 
will allow. And were we to regard external form, we should 
find a stumbling-block at the very threshold of the enquiry: 
where, for instance, shall we detect a similarity between 
birds and cartilaginous fishes, unless we can conscientiously 
pin our faith on such superficial resemblances as that of 
the fossil Pterichthys ? “ Of all the organisms of the sys¬ 
tem, one of the most extraordinary, and in which Lamarck 
would have most delighted, is the Pterichthys, or winged 
fish, an ichthyolite which the writer had the pleasure of 
introducing to the acquaintance of geologists nearly three 
years ago, but which he first laid open to the light about 
seven years earlier. Had Lamarck been the discoverer, he 
would unquestionably have held that he had caught a fish 
almost in the act of wishing itself into a bird. There are 
wings which want only feathers, a body which seems to 
have been as well adapted for passing through the air as 
the water, and a tail by which to steer.”* This similarity 
is, however, no better than imaginary. 
I am well aware how strenuously quinarian systematists 
have insisted on the superficial resemblance existing be¬ 
tween the beak of a bird and that of a tortoise, but I can¬ 
not think such similarities sufficient to justify an approxi¬ 
mation of these groups. A bird is the swiftest, a tortoise 
the slowest of animals : the blood of a bird is remarkable 
for its heat and the briskness with which it circulates, that 
of a tortoise for its coldness and sluggishness: the respi¬ 
ration of a bird is remarkable for its perfection, that of a 
tortoise for its imperfection : a bird is most susceptible of 
hunger and thirst, a tortoise most enduring : a bird is most 
* ‘The Old Red Sandstone; or New Walks in an Old Field.’ By 
Hugh Miller. Ed. 2. 1842, p. 70. 
