Ill] OF BODILY WEIGHT 71 



steadily, and the young woman of twenty is nearly 15 per cent, 

 lighter than the man. This ratio of difference again slowly 

 diminishes, and between fifty and sixty stands at about 12 per 

 cent., or not far from the mean for all ages; but once more as 

 old age advances, the difference tends, though very slowly, to 

 increase (Fig. 6). 



While careful observations on the rate of growth in other 

 animals are somewhat scanty, they tend to show so far as they 

 go that the general features of the phenomenon are always much 

 the same. Whether the animal be long-lived, as man or the 

 elephant, or short-lived, like horse or dog, it passes through the 



80 90 

 years 



Fig. 6. Percentage ratio, throughout life, of female weight to male; 

 from Quetelet's data. 



same phases of growth*. In all cases growth begins slowly; it 

 attains a maximum velocity early in its course, and afterwards 

 slows down (subject to temporary accelerations) tow^ards a point 

 where growth ceases altogether. But especially in the cold- 

 blooded animals, such as fishes, the slowing-down period is very 

 greatly protracted, and the size of the creature would seem never 

 actually to reach, but only to approach asymptotically, to a 

 maximal limit. 



The size ultimately attained is a resultant of the rate, and of 



* There is a famous passage in Lucretius (v, 883) where he compares the course 

 of life, or rate of growth, in the horse and his boyish master : Principio circum 

 trihus actis imfiger annis Floret equus, puer hautquaquam, etc. 



