180 THE PHYSOPODA. 



between which, on the upper surface of the head, we 

 usually find three ocelli. Between the eyes, on the 

 front of the head, the antennse are inserted; these 

 are tolerably elongated organs, composed of from five 

 to nine joints, the latter number being the true one 

 in most cases, although it is often apparently reduced 

 by the amalgamation of some of the apical articula- 

 tions. At the bottom of the head is the mouth, 

 which is closed in front by a large triangular labrum. 

 The thoracic segments are distinctly separated, and 

 each furnished with a pair of short, but strong legs, 

 terminated by tarsi composed of two joints, but 

 destitute of claws, the second bearing instead a small 

 vesicular organ, which acts in the manner of a cup- 

 ping-glass in enabling the little creatures to retain a 

 firm hold of any object upon which they may be 

 walking. It is from this structure that the name 

 Physopoda given to the group is derived. Besides 

 these limbs, the two hinder thoracic segments are 

 also furnished each with a pair of wings in most of 

 tliese insects, and the structm^e of these organs is 

 often exceedingly beautiful. They are usually of 

 equal size and very narrow, and lie over each other, 

 or in juxtaposition along the back of the insect ; their 

 edges are furnished with an exceedingly delicate 

 fringe of fine hairs, sometimes of considerable length, 

 which most frequently extends round the whole mar- 

 gin*. This character, however, is not universal ; some 

 of the Physopoda being totally destitute of wings in 

 the perfect state, whilst in a few species these organs, 

 although present, are greatly abbreviated. 



* From this peculiarity of structure, Mr. Haliday, in his admi- 

 rable memoirs on these insects in the Entomological Magazine 

 (vols. iii. and iv.), proposed to call them Thysanoptera. 



