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 



Pigs. 5-8. Numerical lines of fishes and cetaceans. The " entering angle " 

 begins at the 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 caval/a. 7. Humpback whale, Megaptera. longimana. 

 8. Striped bass, Labrax lineatus. (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- 



