THE 
AMERICAN NATURALIST 



Vor. XXXVI. November, 1902. No. 431. 


BIOMETRIC EVIDENCE IN THE PROBLEM 
OF THE PAIRED LIMBS OF THE 
VERTEBRATES. 
BASHFORD DEAN. 
From early development onward a fish is accurately poised 
in its living medium. Its long axis ina position of rest remains 
normally horizontal, in spite of the most varied changes in 
the size and shape of the fish’s body and the shiftings and 
differentiation of its component parts. To preserve an accu- 
rate balance under conditions of rest as well as under the strain 
of the most active movement implies obviously a delicate 
adjustment of the morphological elements of the animal to the 
physical ones. And as the latter are relatively constant it fol- 
lows that the acute strain in the evolution of the fish’s body, 
both in ontogeny and phylogeny, has fallen upon the mor- 
phological elements. These, then, become subject to form 
changes, to position changes, and, most important, to physio- 
logical changes, to enable them to fulfill the mechanical require- 
ments of habitat. To what degree the results are successful 
in adapting the vertebrate body to aquatic living can best be 
understood by comparison of the “area curves” and “entering 
; 837 T 
