ANATOMY AND PHYSIOLOGY 35 



highly complex suctorial apparatus, as follows. The tongue is a long 

 flexible organ, terminating in a " spoon" (Fig. 127) and clothed with hairs 

 of various kinds, for gathering nectar or for sensory or mechanical pur- 

 poses. The maxillae and labial palpi form a tube embracing the tongue, 

 while the epipharynx fits into the space between the bases of the maxillae 

 to complete this tube. Through this canal nectar is driven, by the ex- 

 pansion and contraction of the tube itself, according to Cheshire, except 

 that when only a small quantity of nectar is taken, this passes from the 

 spoon into a fine " central duct," or also into the "side ducts," which are 

 specially fitted to convey quantities of fluid too small for the main tube. 

 For a detailed account of the highly complex and exquisitely adapted 

 mouth parts of the honey bee, the reader is referred to Cheshire's admir- 

 able work or to Packard's Text-Book. 



FIG. 54. Mouth parts of the honey bee, Apis mellifera. a, base of antenna; br , brain; c, 

 clypeus; h, hypopharynx; /, labrum; lp, labial palpus; m, mentum; mo, mouth; mx, maxilla; 

 sm, submentum. After CHESHIRE. 



Segmentation of the Head. The determination of the number of 

 segments entering into the composition of the insect head has been a 

 difficult problem. As no segment bears more than one pair of primary 

 appendages, there are at least as many segments in the head as there are 

 pairs of primary appendages. On this basis, then, the antennae, man- 

 dibles, maxillae and labium may be taken to indicate so many segments; 

 but in order to decide whether the eyes, labrum and hypopharynx repre- 

 sent segments, other than purely anatomical evidence is necessary. The 

 key to the subject is furnished by embryology. At an early stage of 

 development the future segments are marked off by transverse grooves 

 on the ventral surface of the embryo, and the pairs of segmental appen- 

 dages are all alike (Fig. 195), or equivalent, though later they differen- 

 tiate into antennae, mouth parts, legs, etc. Moreover, the nervous sys- 

 tem exhibits a segmentation which corresponds to that of the entire in- 



