NO. 13 LABIUM OF COLEOPTEROUS LARVAE ANDERSON 5 



more generalized forms. The term second prementum shows that it 

 is a part of the prementum, to which it belongs. 



In order to clear up any confusion that the preceding discussion 

 may have caused, the possibilities of subdivision in the labium of the 

 larvae of Coleoptera, based on the facts as actually observed, are 

 shown in the following table, 



fPrementum J ^'''^ prementum j Prementum 



Labium J L Second prementum / 



IPostmentum Postmentum /Mentum 



l^Submentum 



In the forms studied there was found no example of a labium 

 consisting of four parts, i. e., a first prementum, a second prementum, 

 a mentum, and a submentum. In no case did a true mentum occur 

 together with a second prementum. The first prementum corresponds 

 to the prementum of previous students of these larvae. It carries the 

 palpi, and in nearly all forms the ventral adductors of the labium are 

 inserted on its base. 



In the drawings of the labia, representing the various families, the 

 ventral muscles only have been shown, with a few exceptions. These, 

 the ventral adductors of the labium, and the retractors of the pre- 

 mentum (when present) definitely determine the morphological rela- 

 tionships of the divisions of the labium and serve as criteria for 

 defining them. 



The gular region in the larvae of Coleoptera has been the subject 

 of considerable difiference of opinion as to its definite boundaries. 

 Crampton (1921) shows that in certain insects (termites and others) 

 the gula and submentum are fused into a single " gulamental plate ", 

 and that the posterior portion of this sclerite, fused with the head, is 

 the gula. The conspicuous elongation of this region in certain cole- 

 opterous larvae (as for example Tenebrionidae, pi. 5, C) has been 

 shown by Snodgrass to be an adaptation for preserving the vertical 

 plane of the foramen magnum in the development of the prognathous 

 type of head. 



The gula is defined by Boving and Craighead (1932) as the " area 

 behind submentum, separated from this by a real or imaginary suture 

 between posterior articulations of the two cardines." Since, however, 

 there are numerous cases (Meloidae, pi. 7, C) in which the retractor 

 muscles of the prementum originate on the anterior portion of this 

 area, that part from which these muscles arise should be considered 

 as at least making up a part of the postmentum. For this reason it 

 is preferable to consider the gula as the area between the anteriorly 

 extended lower ends of the postoccipital suture lying behind a line 

 drawn between the posterior tentorial pits. 



