NUMERICAL LINES 5 
line; the dorsal blood-vessel takes its position immediately 
below the vertebral axis, and the air-bladder in the most 
dorsal part of the abdominal cavity. 
FIG. 5 
a 
‘Rigs. 5-8. — Numerical lines of fishes and cetaceans. The “entering angle” 
! 0 Selly snout-tip at the right, and extends as far as the vertical dotted line 
___ (36 %, about, of the entire length) ; the “run” then begins and is continued to the 
body terminal. 5. Striped porpoise, Phocaena lineata, 6. Spanish mackerel 
(Cuban), Scomberomorus cavalla. 7. Humpback whale, Megaptera longimana, 
8. Striped bass, Zadrax /ineatus. (All figures after PARSONS.) 
____ In acquiring this perfect outward symmetry it is inter- 
_ esting to note that the forms of fishes may be said to have 
| _ actually evolved the practical solution of the most theoretical 
_ problems of curves and displacement in relation to sub- 
