90 



ABDOMEN OP INSECTS, AND ITS APPENDAGES. 



replaced by two small moveable threads, thickened at the end, 

 which are called balancers (Fig. 305). 



609. The abdomen of Insects is composed of a considerable 

 number of rings, moveable upon each other ; we can frequently 

 reckon nine of these ; but at other times we cannot distinguish 

 so many ; this appears to depend on the union of two or more 

 of these segments with each other. In the perfect Insect, these 

 rings never bear any legs or wings ; but those which occupy the 

 posterior extremity of the body, often give attachment to ap- 

 pendages, whose forms and uses vary very much. Sometimes 

 they are simple bristles, or points, whose functions are not well 

 known; as in the Ephemera (Fig. 334) for example. Sometimes 

 these organs possess the form of hooks ; and 

 constitute a more or less powerful pair of pin- 

 cers, as amongst the Forficulce, or Earwigs 

 (Fig. 306). At other times they are so 

 arranged, as to act as a spring, and to enable 

 the animal to throw itself forwards; the 

 Podurce, or Spring-tails, small insects, 

 which, in our climate, conceal themselves 

 under stones, or keep themselves on the sur- 

 face of still water, and which also live some- 

 FIG. 306 FORFICULA. ti mes m * ne snow of the coldest regions of the 

 globe, show this mode of organisation. 

 Again, in other instances, these abdominal appendages 

 have a more complicated struc- 

 ture, and constitute an offensive 

 weapon, or an apparatus des- 

 tined to effect the deposit of 

 the eggs laid by the animal in 

 a place fitted for the development 

 of its young ; as examples of 

 these organs, we may mention 



the retractile sting of the Wasps and Bees, and the piercer of 

 the Tenthredos, or Saw-flies. The former is composed of a 

 dart, formed of two sharp-pointed processes, placed within a 

 horny sheath, or case, and having in each a furrow (completed 

 into a canal by the union of the two) through which the poison 



FIG. 307. PODURA. 



