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was only when I noticed that the so-called labrum was divided 

 into two, and that each portion had independent motion, that I 

 discovered that what I called the labrum was the mandibles ; 

 but now I was as much at a loss to account for the presence of 

 the mandibles in this anomalous position as before for their ab- 

 sence. The place of their attachment is under the clypeus, 

 at the margin of the front. The clypeus is apparently absent, 

 but a specimen of the larva prepared for the microscope shows 

 a small piece which is no doubt the clypeus. When this piece 

 is removed, the manner of the hinging of the mandibles is eas- 

 ily seen, but it is necessary to have the head transparent and 

 properly mounted to see it to advantage. In such a specimen, 

 a rather broad, thickened line will be seen on each side of, and 

 somewhat distant from, the middle line of the head ; these two 

 lines are on the interior surface and do not appear at all in the 

 opaque specimen. They diverge rather broadly behind and 

 terminate anteriorly at the clypeal suture ; at this end there is 

 a cavity which receives a short, stout process proceeding from 

 the mandibles on their outer, or, in this position, posterior sur- 

 face, at about one fourth their length from their extreme base. 

 Two slender, rather long processes are produced forward from 

 the space between the ends of the lines ; these, in their natural 

 position, I think, have a somewhat downward curve ; in the 

 specimen under examination they are pressed flat. The man- 

 dibles are divided from their base for about one third of their 

 length to receive these processes, which are produced through 

 them. These last mentioned processes I suppose to be points 

 of muscular attachment. The mandibles are rather slender and 

 acute at the tips ; they have a very strong downward curve, 

 but only a slight outward curve, with the tips pointing directly 

 forward. Looked at directly in front, in the living insect, the 

 mandibles form two sides of a rather acute triangle with its 

 narrowly truncate apex at the middle line of the clypeus. 



From their position, their manner of articulation, and their 

 form, one would be led to think that the mandibles could not 

 have the usual lateral action, and such is the case. The only 

 motion they have is a vertical one, but it is possible that they 

 move on a curve ; if the slender processes in front are 



