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HYMENOPTERA 



submentum is articulated with the mentum in such a manner that 

 the two can either he placed in planes at a right angle to one 

 another, or can he brought into one continuous plane, and by this 

 change of plane the basal part of the tongue can also he thrust 

 forwards. There is considerable variety in the lengths of these 

 parts in different genera, and the lorum varies in shape in accord- 

 ance with the length of the submentum. The lorum is a 

 peculiar piece, and its mechanical adaptations are very remark- 

 able; usually the base of the submentum rests in the angle 

 formed by the junction of the two sides of the lorum, but in Xylo- 

 copa, where the submentum is unusually short, this part reposes 



Fig. 7.— Side view of basal portions of proboscis of Bombus. a. Epipharyngeal sclerites ; 

 b, arrow indicating the position of the entrance to pharynx, which is concealed by 

 the epipharynx, c ; d, hypopharyngeal sclerites ; c, vacant space between the scales 

 of the maxillae through which the nectar conies : /, lobe ; ./'', stipes ; </, cardo of 

 maxilla : h, encephalic pillar on which the cardo swings ; i, angle of junction of lores 

 and submentum lorum ; k, mentum ; /, base of labial palp ; m, maxillary palp. 



in a groove on the back of the lorum, this latter having a very 

 broad truncated apex instead of an angular one ; in the condition 

 of repose the apex of the lorum rests in a notch on the middle of 

 the back of the oral groove, and in some of the forms with elon- 

 gate submentum, this depression is transformed into a deep hole, 

 or even a sort of tunnel, so as to permit the complete stowing 

 away of the base of the tongue, which would otherwise be pre- 

 vented by the long submentum ; another function of the lorum 

 appears to be that, as it extends, its arms have an outward thrust, 

 and so separate the maxillae from the labium. In addition to 

 these parts there are also four elongate, slender sclerites that are 

 only brought into view on dissection, and that no doubt assist in 

 correlating the movements of the parts of the mouth and hypo- 



