THE FRONT COXAL CAVITJKS OK A I'.lCK'rMC. 



15 



tho front co.rdi cavil ics and are eithoi- "entire" when tliey are eii- 

 elosed hcliitid by tlie junetioii of the ])f(>sternuiii and the epimera 

 (the e|)is(erna iievei- reaeliin^' Ihe coxjd cavities proper), or are 

 "open behind" wlien n s[)a('e is U'l'l |)i'o1e('ted only by a menil)i-ane. 

 The\- are "separate" when the ])i'osternnni extends between tlieni, 

 or "continent" when it is not visible l)etween them. 



a b c 



Fig. 4;i. i>. indiciitos tlu' prosteriuiin ; cc, the coxal cavities; is. tlii' tlioracic siclc- 

 picc-os. In a the coxal cavities are widelj t;pcn behind and confluent; in b they are 

 narrowly open behind and separate; in c they are closed behind and separate. 

 (After Wickham.) 



TIk Mvso- and Mctatltorax. The middle or second thoracic seg- 

 ment is called the nicsotliorax, and in the beetles is very closely 

 nnited with the third or hindmost one, the inctafJiom.r. These two 

 form tlie trnnk or main body of the insect, and snpport on their nn- 

 der snrface the middle and hind le.u's and on the sides above the 

 inner wind's and elytra. The upper surface of these two segments 

 is for the most part covered by the elytra and therefore invisible. 

 It consists of fonr pieces, only one of \vhicli, the scu fell inn, a small, 

 shield-shai)ed or triangular plate, is usually visible fi'om above be- 

 tween the bases of the elytra. The mesothorax is much reduced in 

 size, its chief function being to support the elytra and to help keep 

 tliem together by means of its scutellum. 



The ventral or low^er portions of these segments consist of the 

 same pieces as the prothorax, viz.. the niesostcrnum with its side- 

 pieces or episterna and epimera, and the metasternuni, with the 

 same. These pieces are usually distinct, except that the two of each 

 segment are often united to form a single piece. The suture which 

 separates the side-pieces of the raesosternum from those of the me- 

 tasternum is always present. The form and size of these side-pieces 

 is a character much used in classification. 



The Wings. The great majorit\' of adult beetles ])ossess two 

 pairs of wrings. The first or outer pair, known as the elytra (sin- 

 gular elytron), or wnng covers, are present, except in a few females 

 of the family Lampyrida^, are horn-like in texture and vary greatly 

 in shape ami sculpture. They are attached to the mesothorax and 

 usually cover tlu^ upper surface of the abdomen, but in many genera 

 [2—23402] 



