EXTERNAL ANATOMY OF INSECTS. 411 



the same may be said of its appearance in the Trpulce ; but in 

 Musca it is so completely anchylosed with the metathorax as 

 scarcely to admit the possibility of drawing the boundaries of 

 either. In Hymenoptera it also varies in the bees, wasps, 

 Spheces, &c. It forms the anterior portion of what is commonly 

 called the peduncle, and has been noticed by Latreille in some 

 of the Hymenopterous parasites, the peduncle of which he 

 considers as composed of two segments ; and in MacLeay's 

 figure of PoUstes, I believe, the postscideUum (and perhaps 

 scutelliim) of the metathorax, are referable to it. In Sirex it 

 is distinct and free. In Coleoptera it is always anchylosed to 

 the metathorax. In Orthoptera it is always distinct. In 

 most Hemiptera it is anchylosed to the metathorax, though 

 distinct and free in Cicada ; its articulation, however, to the 

 metathorax, whether anchylosed or distinct, is always, as far 

 as I have observed, perfectly immoveable.^ 



The PODEON, or peduncle, is the sixth segment. In Lepi- 

 doptera and Tipula it is rather of less circumference than the 

 adjoining segments ; its articulation with the neighbouring 

 segment on each side is of the mixed kind. In the Muscce, 

 and the majority of the Hymenoptera, it is a mere tube con- 

 necting the incrassated parts of the insect, and its articulation 

 to the propodeon is perfectly free and moveable. In the 

 Tenthredinites, Sirex, and the Coleoptera, neither its articu- 

 lation nor development differ from those of the following 

 segments. The same may be said of its appearance in 

 Orthoptera and Hemiptera, except that in the Cimicites, in 

 common with the other segments, its articulation is almost or 

 quite immoveable. 



The seventh segment, metapodeon, presents no remarkable 

 character except in those Diptera and Hymenoptera in which 

 the podeon is so remarkably restricted : in these its circum- 

 ference anteriorly is not more than one-eighth of its circum- 

 ference posteriorly. 



The eighth segment, octoon, is remarkable for its immense 

 development in the pedunculated insects above spoken of; 

 the common hornet or wasp are good illustrations of this. 



The ninth, tenth, and eleventh segments present but trifling- 

 variations, and these by no means confined to the classes. 



K Great uncertainty exists on this subject, but the jjosition of the spiracle is in 

 favour of the supposition. 



