The Life-History and Anatomy of Butterflies 
plete tube, which is known as Vat proboscis, and which, when not 
in use, is curled up spirally, looking like a watch-spring. At 
Fig. 30 . —Cross-section of the sucking-tube of the 
milkweed butterfly, to show the way in which the halves 
unite to form a central canal (c): tr, tracheae, or air- 
tubes; n, nerves; m, m 3 , muscles of one side. (Magnified 
125 diameters.) (Burgess.) 
the upper end of the proboscis, in the head, is a bulb-like en¬ 
largement, in the walls of which are inserted muscles which have 
Fig. 31.— Longitudinal section of the head of the 
milkweed butterfly: cl, clypeus; nix, left maxilla, 
the right being removed; mfl, floor of mouth; cc, 
oesophagus, or gullet; ov, mouth-valve; sd, salivary 
duct; dm and fm, dorsal and frontal muscles, which 
open the sac. (Magnified 20 diameters). (Burgess.) 
their origin on the inner wall of the head. When these muscles 
contract, the bulb-like cavity is enlarged, a vacuum is produced, 
15 
