OF SUCTION IN LYGUS PABULINUS. 695 
attached (text-figs. 2, 16, Lb.M.). Moreover, it acts as a hinge 
upon which the whole of the labium is bent and doubled. This 
is one of the characteristic features of the insect. In enables 
the insect to get at the required tissues of a plant. The stylets 
are thrust into tissues containing food, the depth of which below 
the surface varies in different parts of the same plant. The 
deeper such tissue lies, the greater is the bend of the labium at 
the first joint. Its bend is scarcely appreciable when the insect 
is sucking sap from tissues which are superficial. 
The stylets cannot be increased in length, but this mechanism 
by shortening the proboscis enables the insect artificially to 
protrude them further into the plant tissue. The labial muscles 
facilitate this bending (text-figs. 2, 16, Lb.M.). 
Text-figure 3. 
Pump-apparatus of Lygus pabulinus. 
Sagittal section. 
For explanation of the lettering see p. 693. 
The second, the third, and the fourth segments are long and 
narrow and gradually taper to a point. The groove, which is 
shallow and flat in the first segment, begins to deepen in the 
