704: EXTERNAL ANATOMY OF INSECTS. 
ants; and also in the Staphylinide to enable them to 
turn up their abdomen like a scorpion, both as a posture 
of attack, and to fold their wings: in all cases, however, 
as far as my observation goes, these animals, when they 
want to lengthen this part, can disengage the rings from 
almost all inosculation, so that no impediment remains 
to any movement. 
The articulation of the dorsal and ventral segments 
with each other is next to be considered. In Julus 
and some Centroti the ring appears to be formed of 
a single piece, with scarcely any trace of the existence of 
any such division; it is however almost universal, and is 
of three descriptions ; in the first the dorsal segments are 
united to the ventral a¢ the lateral margin or edge of the 
abdomen ; in the second it is above this margin, and in 
the third delow it. You will find that in Fulgora and 
many other Homopterous Hemiptera these segments 
unite at the margin, as they do likewise in Czmex lectu- 
larius belonging to the other Hemipterous section ; but 
in the rest of the Heteropterous tribes, the ventral seg- 
ments turn upwards, and their union with the dorsal is 
in the back of the abdomen; in these the Hemelytra and 
wings only cover the dorsal segments, leaving the edge, 
formed of the ends of the ventral, uncovered. The La- 
mellicorn beetles also, and many other Coleoptera, ex- 
hibit the same structure. To the last description, n 
which the dorsal segments turn down to meet the ventral, 
belong the Lepidoptera, Locusta ; likewise Sirer, 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 
