16 THE ANATOMY OF THE HONEY BEE. 



are sometimes separated from both the occiput and the gense and are 

 known as the postgena'. In a few insects, especially beetles, one or 

 two median plates occur in the ventral wall of the head posterior to 

 the base of the labium. These are the gular sclerites. Finally, small 

 plates are sometimes found about the bases of the antennae and be- 

 tween the bases of the mandibles and the genaj. The latter have 

 been termed the trochantins of the mandibles. The term epicranium 

 is often used to include all the immovable parts of the head, but is 

 frequently applied only to the dorsal parts. Most of these sclerites 

 preserve a pretty definite arrangement in the different orders, and 

 they are probably homologous throughout the entire insect series, 

 though they are in some cases very much distorted by special modi- 

 fications and are often in part or wholly obliterated by the disap- 

 pearance of the sutures. Embryologists are coming to the conclu- 

 sion that the sclerites of the head have no relation to the primitive 

 segments. The latter very earlj' consolidate into a head with a con- 

 tinuous wall, while the sutures defining the sclerites are formed 

 later. Some of the older entomologists were led, from a study of 

 the sclerites, to suppose that the head consisted of a number of seg- 

 ments, but it has been shown that these anatomical segments do not 

 correspond with the embryonic ones. 



The appendages growing from the front of the face are the 

 antennae (fig. 9A, Ant) or " feelers " and consist of a series of joints 

 or segments. 



At the lower edge of the face is the front lip or Idbrum (fig. 9A, 

 Lm) , behind which are the median epipharynx, the paired mandibles 

 (Md) and maxilla}, the median hypopharynx, and the labium or under 

 lip. All these organs together constitute what are known as the 

 mouth parts or trophi. They vary greatly in shape and appearance 

 in different insects according to the nature of the food, but their 

 typical form is usually taken to be that shown by the lower insects 

 which feed on solid food and have biting mouth parts. Figure 3, 

 representing the jaws and lips of the common black cricket, is given 

 as an example of generalized insect mouth parts. 



The labium (fig. 9A, Lm) is usually a simple transverse flap in front 

 of the mouth, being developed, as already shown, from a similarly 

 situated lobe on the first segment of the embryo (fig. 2, Lm). 



The epipharynx (fig. 19, Ephy) is a sort of dorsal tongue, and is 

 situated on the membrane leading into the mouth from behind the 

 labrum. 



The mandibles (figs. 3A; 9A, Md) are typically formed for 

 biting, being heavy organs situated immediately behind the labrum 

 and working sidewise on a hinge articulation with the head. Their 

 cutting edges are usually notched and toothed, though smooth m the 

 worker bee. 



