CHAP. XIX. FAMILIES OF NEUBOPTERA. 125 



Family usually have four wings, but the posterior pair are 

 sometimes wanting ; the mouth-parts are obsolete ; the an- 

 tennae are short and three-jointed, and the abdomen is gener- 

 ally furnisfeed at the tip with two or three slender bristles ; 

 the feet have from four to five joints ; transformations incom- 

 plete. After issuing from the pupa the insect is usually 

 enveloped in a thin film, when it is termed the sub-imago; it 

 soon casts off this filmy covering and appears as the perfect 

 insect or imago. The larvae are aquatic, and feed upon other 

 insects, etc. ; they are supposed to remain from two to three 

 years in the larva state, although the adults live but a few 

 hours. These flies quite closely resemble the Ichneumon-flies 

 (Fig. 131), but their antennae are much shorter, and their 

 bodies weaker. 



DRAGON-FLIES (Libellulidse; also called Odonata). These 

 insects are provided with four wings of nearly equal size (Fig. 

 143) ; the antennae are inconspicuous, and from four to seven- 

 jointed ; the feet are three-jointed, and the abdomen is destitute 

 of anal bristles ; transformations incomplete. The larvae are 

 aquatic and feed upon other insects ; they have a peculiar 

 syringe-like apparatus beneath the posterior part of the body 

 by which they are enabled to draw in a small quantity of 

 water and then, forcibly, to eject it backwards, thus driving 

 themselves forward at a rapid rate. 



These insects are divided into two groups, viz. : 



Agrioninse, in which the head is very broad ; the eyes are wide 

 apart, and the wings, when at rest, are raised over the back. 



Libellulinas, in which the head is nearly globular ; the eyes 

 usually touch each other, and the wings are expanded when 

 at rest (Fig. 143). 



SIALIS-FLTES (Sialidae). These insects are provided with 

 four wings of nearly equal size ; the antennae are conspicuous, 

 and the feet are four or five-jointed ; transformations complete. 

 The larvae are predaceous ; some are aquatic, while others live 

 upon trees, etc. In some species the pupa is capable of mov- 

 ing about, although enveloped in a thin covering or skin. 



