GENERAL NOTES ON INSECTS. 323 



B. With mouth-parts adapted in the main as suctorial 



organs (Menorhynchous), usually with no metamorphosis 



(Ametabolic). 



e.g. Rhynchota or Hemiptera, e.g. Phylloxera, aphides, 

 coccus insects ; Cicadas ; bugs ; water-scor- 

 pions, lice. 



C. With complete metamorphosis (Holometabolic), with 



mouth-parts always adapted for biting (Menognathous), 

 or adapted at first for biting and afterwards for sucking 

 (Metagnathous). 



e.g. Coleoptera (beetles) ; Diptera (two-winged flies) ; 

 Lepidoptera (butterflies and moths) ; Hymen- 

 optera (ants, bees, and wasps). 



GENERAL NOTES ON INSECTS. 



The main characteristics of insects have already been 

 described in the two types chosen, but we here revise them 

 in general terms. 



Form. The body of an adult insect may be divided into 

 three distinct regions :- 



1. The undivided head, which consists of at least three fused seg- 



ments, as it bears three pairs of appendages besides the antenna-. 



2. The median thorax, divided into pro-, meso-, and meta-thoracic 



segments, each with a pair of legs, the last two often with wings. 



3. The abdomen with about eleven rings, usually without trace of 



limbs. 



Within these limits there is great variety of form, e.g. the long dragon- 

 fly with its large outspread wings, the compact cockchafer, the thin- 

 waisted wasps and long-bodied butterflies, the house-fly and cricket, 

 the large moths and beetles, and the almost invisible insect parasites. 



Appendages. Insects feel their way, test food, and 

 apparently communicate impressions to one another, by 

 means of the antennas, which some authorities regard as 

 pre-oral outgrowths, not as true appendages. Then follow 

 the mandibles, first maxillae, and second maxillae, on the 

 head; the three pairs of legs on the thorax; and some- 

 times vestiges of legs on the abdomen. 



It was a step of some importance in morphology when Savigny 

 showed that the three pairs of appendages about the mouth are 

 homologous with the other appendages, i.e. are masticatory legs. 



1 I ) Farthest forward lie two mandibles, the biting and cutting jaws. 

 These are single-jointed, and thus differ from the organs of the same 

 name in the crayfish, which bear a three-jointed palp in addition to the 

 hard basal part. In those insects which suck and do not bite, e.g. adult 

 butterflies, the mandibles are reduced. 



(2) Next in order is \hzfirst pair of maxilla. Each maxilla consists of 



