14 Psyche [February 



ponding positions. The cutting edges of both mandibles are 

 beveled in exactly the same manner, on the same side, so that 

 were the cutting edges brought together, the point of each tooth 

 on one mandible would come into direct contact with the corres- 

 ponding tooth on the opposite mandible. Upon a moment's 

 reflection it is clear that such an arrangement would be utterly 

 useless as an organ of mastication. By the use of an ordinary 

 lens one can easily see that such is not the structure, but that the 

 mandibles of the cockroach have their cutting edges quite different 

 the one from the other. Both have toothed edges; but the^ corres- 

 ponding teeth on the different' mandibles are not exactly alike 

 and never borne in the same position ; and are so arranged that 

 those of the left mandible overlap those of the right mandible. 

 This is accomplished by both cutting edges being beveled, the 

 one in the opposite manner from the other so that in coming to- 

 gether they form a crushing apparatus. This structure I have 

 taken pains to show in the accompanying drawing (fig. 1), made 

 from a specimen. 



Insects more commonly used to illustrate the mouthparts of 

 the class are the locusts. The mandibles of Melanoplus femur- 

 ruhrum as represented in Linville & Kelly's General Zoology, 

 or Comstock's Manual of the Study of Insects; and those of Schisto- 

 cerca americana represented in Sanderson's Insect Pests of the 

 Farm, Garden and Orchard, all present the same kind of error as 

 that pointed out in the preceding paragraph. All show the 

 two mandibles exactly, or very nearly alike. Unfortunately this 

 error is of such a nature as to obscure the highly specialized 

 structure of these organs for their function of mastication, for the 

 drawings referred to above more nearly represent the true nature 

 of the mandibles of carnivorous insects than those of the vegetable- 

 eating locusts. I have examined many specimens upon this point, 

 representing no less than forty different species and I herewith 

 present several drawings which I have made from specimens 

 selected from various species to show the variations which occur 

 in the mandibles of the locusts. The drawings are made from 

 mandibles mounted in the same position as when closed in the 

 living specimen; but separated enough to show the grinding surface 

 of the right mandible. 



