THE BOOK OF NATURE STUDY 



can work right up to this ridge ; and when at rest frequently 

 are held thus, one mandible overlapping its fellow for some dis- 

 tance. Since wasps possess no gizzard or other grinding machine 

 along the course of their alimentary canal, all mastication must 

 be accomplished before swallowing takes place ; moreover, the 

 food supplied by the workers to the grubs requires to be reduced 

 to a pulpy condition before it is administered. When the teeth 

 are in use, one set against the other, there is a gap left between 

 the main portions of the mandibles. Into this space, and 

 practically filling it, there projects from the clypeus a small 

 brown oblong structure, the labrum or upper lip, whose lower 



A B 



FIG. 71. Diagram of under side of head of wasp, showing the mouth apparatus. 

 A, retracted ; B, protruded. /, labium ; m, mandible ; m.x. (stipes of) 

 ist maxilla. 



free end is slightly notched, while the upper attached end is 

 drawn out to right and left into a pair of divergent prongs. Thus 

 the whole labrum when isolated is V-shaped. Its entire surface 

 is closely beset with bristles. The remainder of the mouth 

 parts, namely, the two first maxillae and the two united second 

 maxillae (labium), are lodged in the deep depression to which 

 reference has already been made. Their structure, though in 

 the main resembling that of the corresponding organs in the 

 cockroach, is considerably modified, and too complex for detailed 

 treatment here. In order to see these appendages it is best 

 to remove the head and pin it face downwards on a cork, and 

 then examine with a hand magnifying-glass while moving and 

 separating the appendages with a needle. 



