COMPOSITION OF THP: INSECT-CRUST. 



11 



ing the lowest wingless forms such as the Louse, Flea, 

 Fodara, and Bark-lice, where we see a transition to the Or- 

 ders of Spiders and lAIyriopods, that we can perceive tlie plan 

 pervading all these forms, uniting them into a connnon 



clciss. 



A segment of a winged six-footed insect (Ilexapod) consists 

 typicalfy of eight pieces which we will now examine more 

 leisurely. Figure 12 represents a side-view of prm 



the thorax of the Telea PoJiipliemus, or Silk- pt 

 worm moth, with the legs and wings removed. 

 Each ring consists primarily of the tergnm, the 

 two side-pieces (epimerum and episternum) and 

 the sternum, or breast-plate. But one of these 

 pieces (sternum) remains simple, as in the lower orders. The 

 tergum is divided into four pieces. They were named by Au- 



Fig. 12. 



scm ms'' 



■ epm" 



douin going from before backwards, 

 the prcescwfjuu, scutum, scuteUum, 

 and postscutellum. 



The scutum is invariably present 

 and forms the larger part of the «'■ 

 upper portion (tergum) of the tho- '-Pj 

 rax ; the scutellum is, as its name em 

 indicates, the little shield so promi- ^.. 

 nent in the beetle, which is also 

 uniformly present. The other two 

 pieces are usually minute and 

 crowded down out of sight, and placed between the two oppos- 

 ing rings. As seen in Fig. 11, the prjescutum of the moth is 

 a "small" rounded piece, bent vertically down, so as not to be 

 seen from above. In the lowly organized Hepkdus, and some 



FIG. 11. Tergal view of the middle segment of the thorax of 7'elea Polyphemfis 

 prm, priBscutum; ms, scutum: .scm, s,-ntelUnn; ptm, postscutellum; pt, patagium, 

 or shoulder tippet, covering the insertion of the wings. — Onr/i»('l. 



Fir; 13 Side view of the thorax of T. Pohiphemus, the hau-s removed. 1, rro- 

 thoraK • -2, Mesothorax ; .?, Metathorax, separate.! by the wider black Imes. Tergum 

 of the prothorax not represented. m.s-, mesoscutum ; .sc«, mesoscutellum; ms , 

 metascutuui; .scm", metascutellum; /;/, a supplementary piece near the mser- 

 tion of patagia; ,r, pieces situated at the insertion of the wings and surrounded by 

 membrane; em, epimerum of prothorax, the long upright piece above being the 

 episternum; epm, e,.isternum of the mesothorax: em", epimerum of the same; 

 epm-, episternum of the metathorax; em", epimerum of the same, d.vide.l into two 

 pieces; c, c", c" , coxaj; te, h; /e", trochantines ; tr, tr, tr, trochanters. 

 — Original. 



