88 ESSAY ON CLASSIFICATION. Part I. 



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. 

 Everywhere we find evidence that the phenomena of life, though manifested 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 influ- 

 ence 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.^ 



Wlio 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 dui'ation of life and either the size, or structru-e, or habitat 

 of animals ; next, the system, in which the changes occurring during any period are 

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

 formity between the representatives of different classes, within certain limits. 



In most Fishes and the Reptiles proper, for mstance, the growth is very gradual 

 and unifonn, 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 equi- 

 librium, winch lasts for a longer or shorter period in different species. 



In others still, which also acquire within certain limits a definite size, the Mam- 

 malia, for instance, the growth is slower in early life, and maturity is attained, as in 

 man, at an age which fonns a much longer part of the whole duration of life. 



In Insects, the period of maturity is, on the contrary, generally the shortest, 

 while the growth of the larva may be very slow, or, at least, that stage of develop- 

 ment last for a much longer time than the life of the perfect Insects. There is no 



* ScHUBLER, (Gust.,) Beobachtungen iiber jjilir- Thier- und Pflanzenreich, Tiibingen, 1831, 8vo. — 

 liche periodisch wiederkehrende Erscheinungen im Quetelet, (A.,) Phenomenes p^riodiques, Ac. Brux. 



