BATS. 
METAMORPHOSIS OF BIRD TO MAMMAL. 
HE reptilian aspect of the flying pterodactyl, as de- 
• scribed in my introduction to birds, formed a no 
more distinctly pronounced link connecting reptiles 
and birds than the bat furnishes between birds and 
mammals, and is but another of the many proofs 
furnished incontestably demonstrating the evolution 
of species by structural differences to accommodate 
the new births to changed conditions of the earth, 
as already explained. Progression is not always 
evidenced by these new creations, so to speak ; on 
the other hand there appear signs of retrogres¬ 
sion, or deterioration of species, the primitive births 
generally presenting less gracefulness of form and 
less adaptability of structure. Thus we observe in the bat a creature which, 
if regarded as a bird, is unsightly, malformed as a flyer and destitute 
of every economic feature that makes the bird a marvel of perfection in the 
field to which it has been assigned by nature. If we consider the bat as a 
mammal its imperfections are no less pronounced, for which reason the combi¬ 
nation of its bird-like and mammalian characteristics compels its assignment to 
an intermediate class, or a link which binds 
the two orders together. 
With all the seeming faults of structure 
we are able to see in the bat , it is a living 
illustration of the attempts or processes of 
mature towards completing a radical change 
of organization and the development of dis¬ 
tinct and more highly organized species. The 
bat may therefore be regarded as the result 
of a modification of the bird by nature which, 
in the effort to develop into a mammal first 
divests itself of feathers but retains the phal¬ 
anges and wing structure. For the feathers, soft fur, corresponding to down, 
is substituted; or, if we chose to proceed more critically, the quill feathers 
are first removed but the creature is permitted to retain the down. 
The next process is probably conspicuous in the bones of the bird thus 
undergoing metamorphosis. The hollowness of the bones which distinguishes 
the bird gradually changes by the softening of the osseous ducts ramifying the 
cavities until marrow appears, for though the bones of bats are not nearly so 
( 453 ) 
HEADS OF EGYPTIAN BATS. 
