



tral duct," or also in!., 1 he " -ide du< 1 .." \vlii( h are ^>e< ially tit ted to 

 Convey <|iianlitir> <>f thiid tOO -mall for tin- in;iiii tube. For a d< ' 

 Hit Of the highly COmplei and e\<|ui-itely adapted nioutli p.i- 

 tin- honey bee. the reader Ifl referred tn Cheshfc nirable work, 



Packard's 7Y.r/ ttiwk. 01 SlMX I'lir Anatomy of the Honey Bee. 



Segmentation of the Head.- The determination of the number of 

 Moments entering into the composition of th< head bai been a 



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

 appendages, there are at least as many .M-^menN in the head as there are 



8 



FIG. 57. Paramedian section of an embryo of the collembolan Anurida maritima; to 

 show the primitive cephalic ganglia, i, ocular neuromere; 2, antennal; 3, intercalary; 

 4. mandibular; 5, superlingual; 6, maxillary; 7, labial; 8, prothoracic; 9, mesothoracic; a; 

 antenna; /, labrum; /t.labium; f, /*, I 3 , thoracic legs; m, mandible; mac, maxilla. After 

 FOLSOM. 



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 gn 

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

 dages are all alike (Fig. 197), or equivalent, though later they differen- 

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



