1G4 



IXVEKTF.BKATE ANIMALS. 



uir-tubes or traclie;v (fig. Ill), which coiumence at the sui-face by so 

 many apertuies or sjiiracles, and brancli repeatedly as they proceed 

 inwards thr(iu,i,di tlie tissues. They have the same structure a.s in 

 the Ar<icliiujhi, consistai" of membranous tubes strengthened by 



Fi^'. m. — T<liTil tmiisver.se section nf an Insect. Ti Dorsnl vessel; i Intestine; n 

 Vetitral iiei\r-cnr(l : ( ( Stij.nnata leatlin;,' into tliG braiiclierl traclieal tulics ; ww 

 winu's ; a Coxa iif one le;^ ; ?) Troi-iiaiiter ; c Femur ; fj Tiltia ; f Tarsns. (After 

 Pacl<anl.) 



means of a spirally roiled filament of chitine. Tlie trachere are 

 jirolonged into the wings, so that these structure.? likewise assist in 

 respiration. 



Tlje neivous system in insects, tliough sometimes somewhat modi- 

 fled, has essentially the regular Annulose form of a ventral chain of 

 ganglia, traversed in fiaint liy the gullet. The organs of sense are 

 the eyes .-ind .■iiiteniia'. Tlie eyes are usually " compound," and are 

 composed of numerous si.x-sided len.se.s, uiuled together, and each 

 sup]jlied by a separ.-itc nerviius til.-iment. As many as eiglit thousand 

 of these len.ses have been counted in one of the ej'es of the connnon 

 (.'ockchafer, and this number is sometimes greatly exceeded. Besides 

 these ciinipounil eyes there are sometimes " simple " eyes, identical 

 in structuie witli the single lenses of the compound eyes ; and in 

 i;ire cases tliese ;n'e the only organs of vision. The feelera or 

 .•iiitonn:o, with wliich all insects are furnished, are jointed filaments 

 attachod closi- to the eyes, a.nd a-suming very different shapes in 



