114 BEES AND WASPS [CH. 



investigated this matter, state that the poison is 

 formed by the mixture of the secretion of two glands, 

 one of which is acid (formic acid) and the other alka- 

 line. Carlet states that the poison of the Fossors 

 which has merely a stupefactive action is deficient 

 in the alkaline constituent. 



The details of structure are, of course, not iden- 

 tical in the stings of all Aculeates: the shape and 

 internal arrangements of the "director," the form 

 of the "needles," and disposition of the levers all 

 vary in different groups : nor are barb-hooks always 

 present, for the "needles" of the Fossors have none. 

 The presence of barbs frequently results in the sting 

 being left in the wound and all its appurtenances 

 being dragged out of the body, with ultimately fatal 

 results to the insect. 



The tongue of a bee (vide fig. 21, and cf. figs. 9 

 and 10) forms the central, unpaired structure of an 

 otherwise bilaterally symmetrical and rather com- 

 plicated set of mouth parts. On the under and 

 posterior side of the head there is a deep recess 

 occupied by the basal part of this apparatus which 

 fits into it. If the whole structure be pushed forward 

 so as to withdraw the basal portion from the head- 

 recess, it will be found that on each side, right and 

 left of the recess, there is articulated a short rod, 

 slightly swollen and flattened at its apex : these rods 

 are really the basal pieces (cardines) of the (first) 



