EXTERNAL ANATOMY OF INSECTS. 337 



fining its sides or whole circumference. In many cases 

 this margin is broad and dilated, but in others it is merely 

 a thread or bead that separates the shield from the ora. 

 Though generally terminating the upper surface, it some- 

 times, as in Staphylinus, dips below it. In many insects, 

 however, as I just observed, the thoracic shield has no 

 lateral margin whatever. 



3. Various and singular are the appendages with which 

 the prothorax of numerous insects is furnished. Many of 

 these are sexual distinctions, and have been before de- 

 scribed to you a ; but there are others common to both 

 sexes, the most remarkable of which I shall notice. — 

 Some are distinguished by a long horn which overhangs 

 the head, as Membracis cultrata, ensata, &c. b ; in others 

 it stands upright, as in Centrotus spinosus c ; C. Tau- 

 rus has a pair of thoracic horns like those of a bull, 

 only dorsal d ; in Ledra aurita they are flat, and repre- 

 sent ears e ; in some species of Tingis ( T. Echii, Pyri, &c.) 

 a kind of reticulated hood, resembling lace, is elevated 

 from the anterior part of the prothorax, which receives 

 and shelters the head f . In Centrotus globularis and cla- 

 vatus F., especially the former, thepartin question is armed 

 by a most singular and wonderful apparatus of balls and 

 spines, — in one case standing erect s , and in the other be- 

 ing horizontal h , — which gives these animals a most extra- 

 ordinary appearance. In many of the species here quoted 



a See above, p. 327— • 



b Coquebert Illustr. Ic ii. t. xviii./. 2, 4. 



<■ Stoll Cigales t. xxlf. 116. d Ibid. t. xi./. 53. 



e Plate II. Fig. 4. " f Plate XIII. Fig. 18. 



3 Stoll -Cigales t. xxviii./. 163. 



h Ibid. t. xxi.f. 115. Coquebert Must. Ic. ii. t. xviii./, 5. 



