THE BUTTERFLY. 



61 



actual use in extracting honey from flowers ? 

 Some have thought that the upward flow was due 

 to capillary motion ; some to the action of the so- 

 called sucking stomach, a sac-like expansion of 

 the alimentary canal just 

 in advance of the true 

 stomach ; others that it is 

 forced on by successive 

 undulations and contrac- 

 tions of the tube itself. 

 The investigations of one 

 of oar own naturalists* 

 has, however, recently 

 shown the existence of a 

 muscular sac within the 

 head [Fig. 70], at the 

 origin of the alimentary 

 tract, furnished with a 

 valve at its front extrem- 

 ity where it opens into 

 the maxillary canal. 

 When the radiating mus- 

 cles running from the 

 walls of the head to the periphery of this sac are 

 contracted [Fig. 71], the sac is opened, and into 

 the vacuum thus produced the fluids into which 

 the maxillae are plunged ascend. On the relaxa- 



FIG. 69. Longitudinal section of 

 one maxilla of Danais Plexippus to 

 show the interior muscles (m) 

 which coil it and the nerve (ri) and 

 the trachea (tr) which pass through 

 it; X about 125 (Burgess). 



* E. Burgess, Amer. Nat., xiv., 313-319. 



