H YMENOPTERABEES 



f55 



their edges, form a tube out of which only the part nw of the Ugula protrudes 

 (Fig. 67). But almost simultaneously with these movements, the bee retracts the 

 basal part of the ligula into the hollow end of the mentum, and so draws the tip 

 of the ligula, which is wet with nectar, into the tube, where the sweet liquid is passed 

 on by the rapid successive erection of the whorls of hair from the tip towards the base 

 of the ligula, while the simultaneous expansion of an internal cavity in connection 

 with the mouth (indicated externally by a swelling of the abdomen) sucks it in. The 

 process of sucking as described in the humble-bee can readily be detected by noting 

 the expansion and contraction of the abdomen, so that it is easy to see whether a 

 flower which the bee is beginning to suck has already been drained of nectar or not. 

 (Cf. also my remarks on the visit of Anthophora pilipes F. ( = Poda]irius acer- 

 vorum L.) to Lamium purpureum Z., p. 166.) 



Fig. 66. Head of hn7nbh-bee (after Herm. Muller). (i) Head of Bombus agrorum F. 9, with 

 completely extended and widely separated mouth-parts; seen from above (x 5). (2) Mouth-parts of the 

 honey-bee in the same condition ; seen from below (x 12). pl\ The two basal joints of the labial palps, 

 which are modified to form part of the ligular sheath ; w^ the membranous lappets at the tip of the ligula ; 

 X, the piece which covers the mouth-opening, which lies between mt and x 1 epipharynx, Westwood); 

 y, submentum, the chitinous piece which lies at the base of the mentum, and continues it backwards 

 (fulcrum, Kirby) ; z::, retractors, chitinous pieces which unite the submentum with the ends of the cardines, 

 cc, and, as they revolve backwards round the ends of the cardines, retract the mentum and all its 

 appendages (Kirby calls ::z cardines, and cc lora). 



' The sucking of nectar,' says Hermann Muller (' Wechselbeziehungen,' pp. 29, 30), 

 ' is prejudiced to an unknown extent by an imperfection in the adaptation, i. e. the 

 character of the nectar can only be recognized after the entire space between the 

 hairy ligula and its sheath has been filled with fluid, and this has risen as far as 

 the taste-organs. Should it then appear to the bee that the nectar is not agreeable, 

 sucking may cease, but this will not get rid of the layer adhering to the whorls of 



