102 MAINE AGRICULTURAL EXPERIMENT STATION. I902. 



The labrum is triangular in shape, but quite unsymmetrical. It 

 is longer on the right than on the left side, the greater part of the 

 attachment of the base of the labrum being on the right side of 

 the median line of the head. 



The parts which have been described by most American 

 writers as mandibles are slender bristle-like spines, each of which 

 has an enlargement at its upper end. They are situated inside of 

 the mouth, and when in use extend through the oral aperture. 

 Sections of the head clearly show, as has been mentioned by 

 Garman,* that the upper broad end of these parts are joined to 

 the maxilla 4 by a short round basal piece. There is a distinct 

 joint between these two parts. 



The maxillae are elongated, triangular in shape, and placed 

 so that they form the lateral borders of the mouth. Near their 

 middle point there is a three-jointed palp. 



The labrum is made up of two thickened portions which lie 

 at the side of the mouth below the maxillae, and a third ventral 

 portion connecting the thickened parts. It bears on its lower 

 third a pair of three-jointed palps. The palps bear spines on 

 the distal end of each joint. 



On the left side of the head there is a single unpaired organ, 

 shaped somewhat like one of the piercing setae, only it is stouter 

 and has the upper portion much thicker. There is nothing on 

 the right side of the head to correspond to this organ except, in 

 some cases a small papilla. 



Inasmuch as the piercing setae are composed of two portions 

 united by a joint, they are not homologous with the mandibles 

 of other Hexopoda, which are in all cases composed of a single 

 piece. They should rather be regarded as specialized lobes of 

 the maxillae. 



The unpaired organ has been interpreted by some writers as 

 an epipharynx which has been shifted to one side. Others con- 

 sider it to be the left mandible, the right mandible being wanting 

 or rudimentary. 



Considering the modification of the parts, and the apparent 

 deficiency of the right side of the head, it would seem that the 

 latter is the most reasonable interpretation. 



* Garman, H.— The assymetry of tlie Mouth-parts of the Thysanoptera, American 

 Naturalist, Vol. XXX, July, 1896. 



