INSECTS. 285 



white, sometimes pale red or brown-yellow, and are not surrounded 

 by a fibrous membrane, so that, when detached from their inser- 

 tions, they may be spread out like a pencil. 



Many insects are distinguished by special art-instincts, by their 

 cunning in overpowering their prey, by the care for their eggs or 

 young, by the construction of artificial habitations, &c. Their 

 field of observation is greatly extended by the high development of 

 heir visual organs. The faculty of indicating beforehand changes 

 >f the weather by certain actions, by which some insects are dis- 

 inguished, rests probably on their finer sense of the different con- 

 itions of the atmosphere, since the air penetrates their whole body 

 >y the tracheae. In this respect, as in so many others, they resemble 

 lirds amongst vertebrate creatures, whose air-sacs and hollow bones 

 ire in connexion with the respiratory organs, and in which also 

 perfect correspondence between the external atmosphere and the 

 nternal parts of the body is thus maintained. 



Manifold is the damage which Insects occasion to us, as well 

 >y spoiling our luxuries, as by injuring or annihilating our pro- 

 perty. On the other hand they procure for us many advantages, 

 imongst which I need only name silk, wax and honey. But much 

 nore important still is the use they supply in the great economy of 

 lature, and therefore indirectly to us 1 . The injury which they 

 ometimes cause us, is not only more than counterbalanced by 

 hese benefits, but is for the most part only a consequence of the 

 3eneficent action itself. It is these small animals that nature em- 

 >loys for her great purposes, and which effect by their numbers 

 rhat the largest animals working separately are unable to perform, 

 lence they are less dependent on the will of man, which indeed 

 lere and there may be able to destroy a species, but is unable to 

 sxterminate it throughout entire districts, as it has annihilated 

 Lifferent mammals in lands which they formerly inhabited. Insects 

 maintain the due equilibrium in the vegetable kingdom, diminish 

 )utrefaction, and lastly afford to many other animals, especially 

 )irds, an abundant and ever present nutriment. 



The geographical distribution of Insects opens a wide field for in- 

 quiry, which however has only been lately entered. Many families, 



1 On the benefit and the injury caused by Insects, see in detail KlKBY and 

 SPENCE, Introduction to Entomology, I. pp. 80 338. 



