MOUTH PARTS : TABANUS 23 



on a hand saw. The outer edge of the blade is thickened from the 

 point upwards, and the inner in its proximal half ; at the base the 

 mandible is divided into two strong cornua, the internal one of which is 

 free, the external being articulated to the epicranium at a prominent 

 angle. The muscles of the appendage arise in the floor of the head 

 cavity, and are inserted into the two cornua; those which pass to the 

 internal cornua are the strongest, and act as adductors ; those inserted 

 into the external cornua act as abductors. 



The first maxillae (Plate IV, fig. 4 and Plate V, fig. 4), as is the case in 

 the cockroach, are more complex than the mandibles. Although the 

 appendage is, of course, altered in form for its specialized function, all the 

 parts seen in the simpler insects are present. The blade, which corresponds 

 to the galea of the cockroach, is a stout chitinous rod, quadrilateral in sec- 

 tion in its distal part, but flattened towards the base. It is armed with 

 stout rasp-like teeth, set closely together in an imbricate manner, on the 

 whole of the surface of the distal end, and for some distance on the inner 

 side. All these teeth point towards the base of the blade. The blade is 

 directly continuous at its base with a much convoluted piece of chitin, 

 the stipes, which runs across the floor of the head at the side of the 

 buccal cavity, and is attached to the wall a little in front of the occipital 

 foramen by the interposition of a short stout wedge-shaped rod, the 

 cardo. The lacinia is represented only by a short peg-shaped projection 

 on the inner side of the base of the blade. The palp is well developed. 

 It consists of two joints, a short cylindrical one and a larger conical one. 

 The two palps turn a little forward from their origin, and converge 

 towards one another in front of the proboscis, so as to conceal its upper 

 part when looked at from the front. When the fly is feeding they are 

 directed forwards, away from the proboscis. 



The muscles of the maxilla are arranged in two sets, one of which 

 protracts the blade, while the other retracts it. The protractor fibres 

 arise from the anterior wall of the head capsule, and pass backwards to 

 be inserted into the stipes ; the retractors, which are much stronger, run 

 in the opposite direction, from the neighbourhood of the occipital 

 foramen. 



The method by which these appendages act in the making of the wound 

 will now be evident. The mandibles are rotated inwards on their 

 point of attachment to the head capsule by their adductor muscles, and 

 the blades are thus drawn obliquely across the tissues. They are replaced 

 in position by the abductors. The maxillae are alternately protracted and 

 retracted by two sets of muscles pulling in different directions, and at 



