— 
OF SUCTION IN LYGUS PABULINUS. 73 
(8) The Cardiac Valve. 
The valvular muscles contract, the valve opens, and the sap is 
forced into the stomach. 
(9) fhe Stomach. 
This is a bag-like strueture and stores the sap. 
To sum up :— 
There are the following factors at work :— 
G.) Capillarity in the suction-canal, helped by turgidity of the 
cells. 
(ii.) Suction produced by the vacuum through the raising of 
the operculum. 
(ii.) The peristalsis in the cesophagus by means of the 
constrictors. 
(iv.) The valvular action, which prevents the sap from flowing 
back into the cesophagus from the stomach. 
The pharyngeal duct hangs into the suction-canal and is 
immersed in the sap. A question arises whether it is possible 
for the sap to avoid the duct and flow into the body-cavity from 
the suction-canal. The sap cannot do so because (i.) there is no 
difference of pressure to force the sap into the body-cavity, and 
because (ii.) there is active suction through the pharyngeal duct. 
Another important thing for suction is that the suction- and 
ejection-canals must be separate and distinct from each other. 
The least intercommunication will stop the whole mechanism. 
Also one canal cannot serve two contradictory purposes—one of 
sucking and the other of ejecting saliva. The whole mechanism, 
therefore, depends upon the presence of the two canals. (But, 
curiously enough, the Bed-bug, Cimesx, is stated to present such 
an anomalous case. It has only one canal for sucking the blood 
and ejecting the saliva as well. Recently it has been described 
by Dr. Max Braun (1): “In shape the maxille resemble two 
gutters, the concave surfaces of which face one another and so 
forma tube. This serves to conduct the blood from the wound 
into the pharynx and also saliva into the wound. In other 
Hemiptera food and saliva are conveyed by two distinct channels 
formed by the longitudinal ridge which runs down the groove of 
each maxilla, dividing it into two parts.” This is not the case 
actually, as I hope shortly to show by figuring sections of its 
mouth-parts.) 
Damage to the Plant. 
That Lygus pabulinus does some damage to potato plants 
has been conclusively proved by the elaborate experiments of 
Prof. Lefroy, of the Imperial College of Science, and Mr. Horne. 
It is sufficient to say here that the insect drills into the leaves 
holes which are bordered afterwards by brown rims. It does not 
Proc. Zoou. Soc.—1914, No. L. 50 
