FORM APPENDAGES. 307 



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. 



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. 



But this is only the crude anatomy of form. One must 

 think of the long dragon fly with outspread wings, and of the 

 compact cockchafer, of the thin-waisted wasps and long- 

 bodied butterflies, of house fly and cricket, of large moths 

 and beetles, and the almost invisible insect parasites. 



Appendages. 



Insects "feel their way," test food, and apparently com- 

 municate impressions to one another by means of a pair of 

 jointed feelers or antennae, situated in front of the head. 

 Unlike the organs of a similar name in Crustaceans, the 

 antennae are not usually ranked among the appendages 

 strictly so-called. They seem to be pre-oral outgrowths. 



It was a step of some importance in morphology when Savigny 

 showed that the three pairs of appendages about the mouth were 

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



(i.) Furthest 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 \h.e first pair of maxillce. Each maxilla consists 

 of a basal piece (protopodite), an inner fork (endopodite), and an outer 

 fork (exopodite). I use these names from Crustacean terminology, 



