706 EXTERNAL ANATOMY OF INSECTS. 



of the ends of the ventral, uncovered. The Lamelli- 

 corn beetles also, and many other Coleoptera, exhibit the 

 same structure. To the last description, in which the 

 dorsal segments turn down to meet the ventral, belong 

 the Lepidoptera, Locusta Leach; likewise Sirex, Chrysis, 

 and many other Hymenoptera. The articulation between 

 these segments is by means of an elastic membranous 

 ligament, which usually is not externally visible ; but in 

 many instances, in which the connecting ligament is of a 

 firmer substance, as in Scorpio, Thelyphonus, and Phrynus, 

 it is very conspicuous, and in the latter genus exhibits 

 many longitudinal folds, as it does likewise in Gryllo- 

 talpa, which must permit a vast extension of the abdo- 

 men. In this membrane, in some cases, as in Dynastes 

 M C L., Melolontka, &c, the two or three first spiracles 

 are fixed 3 . In the Hymenoptera and many other insects 

 the dorsal segments do not unite by their margin with the 

 ventral, but the end of each dorsal laps over that of the 

 corresponding ventral. 



Dorsal segments' 1 . I shall next notice the segments 

 seriatim, in the order of their occurrence, beginning 

 with the dorsal ones. The most remarkable circumstance 

 with respect to these that occurs to my recollection takes 

 place in the Cancroid spiders (Epeira cancriformis, acu- 

 leata, &c), in which the back of the abdomen is formed 

 by a plate, in some extended in a transverse direction 

 (E. cancriformis), in others in a longitudinal one (E. 

 aculeata), of a much harder substance than the under 

 side and quite flat, set with strong sharp spines, in the 

 former species apparently moveable, and terminating be- 



a Pi,at£ VIII. Fig. 9. A", E. » Ibid. Fig. 5. A". 



