286 Annals Efitomological Society of America [\'o\. XI, 



The first is a very slight cuticular invagination on each side of 

 the labrum. Both cuticular layers take part in its formation. 

 The mandibular tendon is a long chitinous invagination extend- 

 ing caudo-mesad from the posterior edge of the inner face of the 

 mandible. It is formed almost entirely of the secondary 

 cuticula. The maxillary tendon arises at the end of the chiti- 

 nized portion of the stipes, and extends mesad in a curved line, so 

 as to form a semi-circle. Both layers of chitin contribute equally 

 to its formation. 



Muscles. Two sets of muscle fibres are connected with the 

 labrum. A large muscle fibre runs on each side from the labral 

 invagination to the median dorsal invagination. Their con- 

 traction closes the labrum firmly against the mandibles. The 

 second set consists of five or six fibres which run between the 

 labral invaginations. Their contraction tends to pucker the 

 labrum. There does not seem to be a set of fibres to open the 

 labrum. All of these muscles are cephalad of the oral invagina- 

 tion, and of the supra-oesophageal ganglion. 



The muscles connected with the mandibles occupy the 

 greater part of the head cavity. There are two principal sets. 

 Both are attached to the mandibular tendon ; the flexor muscles 

 extend to the median dorsal invagination, or to the body wall 

 entad of the tendon, while the retractor muscles extend to the 

 cuticula ectad of the tendon. The most cephalic fibres are 

 anterior to the labral muscles, while others extend caudad as 

 far as the oesophageal connectives. There is also a third set of 

 mandibular muscles which are but slightly developed. They 

 are inserted at one end on the cuticula of the outer face of the 

 mandible, and at the other on the cuticula of the body wall at 

 the base of the mandibles. Their contraction would serve to 

 close the mandibles very tightly. 



The maxillary muscles arise on the maxillary tendon and 

 extend to the gula. There are about twenty fibres connected 

 with each maxilla. 



The labial muscles arise on the thickened cuticula at the 

 distal end of the mentum, and are inserted on the gula. There 

 are about five fibres on each side of the labium. 



Attachment. The muscles are attached through the hypo- 

 dermis to the secondary cuticula (or through the epithelium to 

 the secondary intima) both here and elsewhere in the body. 



