times as long as it takes them to reach maturity. 

 Another naturalist, Flourens, later worked over 

 the same ground and asserted that the cessation of 

 growth takes place in the dog at two years of age, 

 in the lion at four, in the horse at five, and in man 

 at twenty. The normal life cycle of the dog being 

 nearly twelve years, and that of the lion and horse 

 twenty-five, it will be seen that these instances 

 represent a period of life the proportion of which 

 is about five times to that of the duration of 

 growth. Accordingly, too, man as a perfectly func- 

 tioning physical machine should live to be a hun- 

 dred, notwithstanding the scriptural formula of 

 "three score years and ten." That he has often ar- 

 rived at an age considerably beyond this, is a 

 matter of common record. 



This proportion of five to one is much increased 

 in the case of birds, and vastly so in that of fishes. 

 But assuming that even no difference exists in the 

 relative proportions between fishes and mammals, 

 it may still be maintained on this ground alone 

 that the sea-horse very likely outlives man. Be- 

 sides, if the actual measured rate of growth of the 

 young captive animal can be relied on, this as- 

 sumption is still further strengthened; for in the 



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