34 



force by which the puncture is made is usually ascribed, somewhat vaguely, 

 to the forward thrust of the body. To put this in more precise 

 terms would be to assert that the muscles of the legs thrust the body 

 forward, and that this force is conveyed to the piercing stylets through 

 the neck. There are two reasons why this cannot occur. In the first 

 place, the neck is anatomically incapable of conveying such a thrusting 

 force, being in most cases almost entirely membraneous ; and even 

 if it could do so, the force would have to act through an angle 

 which is often nearly a right angle, for the proboscis is not directed 

 in line with the body in the position of action, but perpendicular to 

 it. Even the Anopheles mosquito bends its proboscis downwards when 

 it is in use, thus losing any advantage its forwardly directed pro- 

 boscis might be thought to have. The making of the wound is there- 

 fore to be regarded as a function of the appendages, acting by their own 

 muscles, exactly as do the appendages of other arthropods. It might, on a 

 first consideration, be difficult to believe that such minute lancets, actuated 

 by what are after all extremely minute muscles, are capable of making a 

 wound sufficiently deep to draw blood, but the mechanical difficulties 

 are less than they seem. In the first place, one has to remember that 

 rapid contraction is a special characteristic of insect muscle ; according 

 to Marey, the wing of a fly can make 330 contractions per second. 

 If it is admitted that the muscles of the appendages can contract at 

 anything approaching this rate, it is easy to understand how the stylets 

 enter the skin. There is, moreover, no waste of effort, for a deep 

 wound of narrow bore is all that is required, and the stylets are elongate 

 and narrow, having a short and sharp cutting edge. In the second place, 

 the shape and thinness of the stylets does not render them as liable to 

 fracture as one might suppose, for they possess a certain amount of 

 flexibility, probably sufficient to enable them to bend if they meet with 

 any resistant tissue when they are thrust in. As the maxillae, which 

 would appear to be the most liable to this sort of injury, cut mainly in 

 retraction, the stress will tend rather to straighten than to bend the 

 blade. Resistance met with during protraction would bend the blade, 

 but no great resistance is likely to be met with at this part of the 

 cutting action, for the majority of the teeth are always directed towards 

 the base of the appendage. 



The labrum-epipharynx and the hypopharynx are commonly included 

 with the mandibles and first maxillae as piercing stylets, and the 



The Prestomum P rocesses on tne i r distal ends are regarded as teeth. 

 It is most improbable that they take any part in the 



