Ill] OF^SURFACE AND VOLUME 205 



Stork and seagull have a great expanse of wing; but other skilled 

 and speedy fliers have long narrow wings rather than large ones. 

 The peregrine has less wing-area than the goshawk or the kestrel; 

 the swift and the swallow have less than the lark. 



Mean ratio, VS/^^^W, between wing-area and weight of birds 

 {From Mouillard's data) 



Ratio 



To measure the length of an animal is easy, to weigh it is easier still, but 

 to estimate its surface-area is another thing. Hence we know but little of 

 the surface-weight ratios of animals, and what we know is apt to be uncertain 

 and discrepant. Nevertheless, such data as we possess average down to mean 

 values which are more uniform than we might expect*. 



Mean ratio, VS/VW, in various animals [cm. gm. units) 



A further note on unequal growth, or heterogony 



An organism is so complex a thing, and growth so complex a 

 phenomenon, that for growth to be so uniform and constant in all 

 the parts as to keep the whole shape unchanged would indeed 

 be an unlikely and an unusual circumstance. Rates ''^ary, propor- 

 tions change, and the whole configuration alters accordingly. In so 

 humble a creature as a medusoid,. manubrium and disc grow at 

 different rates, and certain sectors of the disc faster than others, 

 as when the little Ephyra-lfnya. "develops" into the great Aurdia- 

 jellyfish. Many fishes grow from youth to age with no visible, 



* From Fr. G. Benedict, Oberflachenbestimmung verschiedener Tiergattungen, 

 Ergebnisae d. Pkysiologiey xxxvi, pp. 300-346, 1934 (with copious bibliography). 



