J 4 EX VI RIB US VIVIMUS. 



Of still lower forms of life there is as little knowledge 

 in most cases as in the higher forms. The Vegetable 

 division of organisms aniong its higher and terrestrial 

 members furnishes ample data ; the ages of trees, 

 shrubs, and such like forms appear to be well 

 ascertained, but those whose condition and struc- 

 ture is diversified by aquatic habitat, leave us as 

 much • in ignorance as do similarly inaccessible 

 animals. 



Here, then, before entering on this enquiry, whilst 

 but looking out on the road, we see how few are the 

 guide-posts — how small the assurance we can have of 

 taking the right turning. When that immense engine 

 of scientific observation, which is wielded by statisti- 

 cians, has been fairly and fully applied to the human 

 species and to such of the many and varied forms 

 of animal life as may be possible, not only so as to 

 determine length, but other quantitative phenomena ^ 

 of life also, then we may hope to see the problem, 

 about to be discussed, definitely and clearly investi- 

 gated by inductive methods. 



^ Such are the time of gestation, incubation, metamorphosis, of hyber- 

 nation, of sleep, of growth, the amount of deaths and births at various 

 ages, of food consumed, of force exerted — phenomena, none of which 

 can be measured or determined by isolated cases, but require, like 

 longevity, the examination of vast numbers to give true results, varying 

 as they may do in the individuals of a species. 



