FUNDAMENTAL RELATIONS OF ANIMALS 89 



servient to their purposes, as in the case of the ostrich. Reptiles and 

 terrestrial Mollusks bury their eggs to subtract them from varying 

 influences; fishes deposit them in localities where they are exposed to 

 the least changes. Insects secure theirs in various ways. Most marine 

 animals living in extreme climates lay their eggs in winter, when the 

 variations of external influences are reduced to a minimum. Every- 

 where we find evidence that the phenomena of life, though mani- 

 fested in the midst of all the most diversified physical influences, 

 are rendered independent of them to the utmost degree by a variety 

 of contrivances prepared by the animals themselves in self-protection, 

 or for the protection of their progeny from any influence of physical 

 agents not desired by them or not subservient to their own ends. 



SECTION XIX 

 DURATION OF LIFE 



There is the most extraordinary inequality in the average duration 

 of the life of different kinds of animals and plants. While some grow 

 and reproduce themselves and die in a short summer, nay, in a day, 

 others seem to defy the influence of time. 



Who has thus apportioned the life of all organized beings? To 

 answer this question, let us first look at the facts of the case. In the 

 first place, there is no conformity between the duration of life and 

 either the size, or structure, or habitat of animals; next, the system 

 in which the changes occurring during any period are regulated 

 differs in almost every species, there being only a slight degree of 

 uniformity between the representatives of different classes, within 

 certain limits. 



In most Fishes and the Reptiles proper, for instance, the growth 

 is very gradual and uniform, and their development continues 

 through life, so much so that their size is continually increasing 

 with age. 



In others, the Birds, for instance, the growth is rapid during the 

 first period of their life until they have acquired their full size, and 

 then follows a period of equilibrium, which lasts for a longer or 

 shorter period in different species. 



