84 INSECTS CHAP. 



that are capable of using the ocean as a medium of existence at 

 a distance from the shore. 



It will probably be asked, how has it come about that creatures 

 so insignificant in size and strength have nevertheless been so 

 successful in what we call the struggle for existence ? And it is 

 possible that the answer will be found in the peculiar relations 

 .that exist in Insects between the great functions of circulation 

 and respiration ; these being of such a nature that the nutrition 

 of the organs of the body can be carried on very rapidly and very 

 efficiently so long as a certain bulk is not exceeded. 



Rapidity of growth is carried to an almost incredible extent 

 in some Insects, and the powers of multiplication which may 

 be considered as equivalent to the growth of the species even 

 surpass the rapidity of the increase of the individual ; while, as 

 if to augment the favourable results attainable by the more usual 

 routine of the physiological processes, " metamorphosis " has been 

 adopted, as a consequence of which growth and development can 

 be isolated from one another, thus allowing the former to go on 

 unchecked or uncomplicated by the latter. A very simple 

 calculation will show how favourable some of the chief features 

 of Insect life are. Let it be supposed that growth of the 

 individual takes time in proportion to the bulk attained, and let 

 A be an animal that weighs one ounce,. B a creature that weighs 

 ten ounces, each having the power of producing 100 young when 

 full grown ; a simple calculation shows that after the lapse of a 

 time necessary for the production of one generation of the larger 

 creature the produce of the smaller animal will enormously out- 

 weigh that of its bulkier rival. Probably it was some considera- 

 tion of this sort that led Linnaeus to make his somewhat para- 

 doxical statement to the effect that three flies consume the 

 carcase of a horse as quickly as a lion. 1 



Astonishing as may be the rapidity of the physiological pro- 

 cesses of Insects, the results attained by them are, it must be 

 admitted, scarcely less admirable : the structures of the Insect's 

 body exhibit a perfection that, from a mechanical point of view, is 

 unsurpassed, while the external beauty of some of the creatures 

 makes them fit associates of the most delicate flowers or no mean 

 rivals of the most gorgeous of the feathered world. The words 



1 Tres muscae consumunt cadaver equi, aeque cito ac leo. Syst. Nat., ed. xii. ref. 

 I. pt. 2, p. 990. 



