24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 



attached to the apex of the subHgular plate (k) at the end of the 

 prementum. The two muscles of the rod (20) are attached by tendons, 

 not directly on the rod, but immediately at the sides of its recurved 

 basal part. It is clear that the contraction of the muscles increases the 

 basal curvature of the rod (I), and therefore pulls the rod back 

 through the tongue as far as the membranous wall of the enclosing 

 channel will permit. The tongue is thus shortened, owing to the 

 compressibility of its ringed wall, particularly in its distal part. On 

 relaxation of the muscles the tongue is again extended, evidently by 

 the elasticity of the rod and the compressed tongue wall, since there 

 is no specific extensor mechanism. Furthermore, the attachment of 

 the muscles at the sides of the rod enables the muscles by acting 

 singly and alternately to revolve the rod, and thus probably are 

 effected the varied lateral movements of the tip of the tongue. 



We may now examine the mechanism by which the base of the 

 ligula is retracted into the end of the prementum and the tongue turned 

 back behind the head in the position it assumes when the proboscis 

 is retracted (fig. 3 B, D). In the functionally protracted condition 

 of the labium (fig. 7 D) the tongue and the paraglossae are extended 

 from the end of the prementum and their bases are fully exposed. 

 In the retracted state (E) the base of the ligula is deeply sunken into 

 the end of the prementum, and the tongue is sharply bent backward 

 behind the latter. It is to be seen also that the ligular arms of the 

 prementum (D, h) have been completely folded inward, and that the 

 subligular plate is angularly bent upward (B, k). The position of 

 the parts concealed by retraction is best seen in a sectional view (A). 



The retraction of the ligula is brought about by two pairs of 

 muscles inserted on the distal ends of the ligular arms of the pre- 

 mentum (fig. 7 A). One muscle of each pair is the long retractor 

 of the labium (77) arising in the top of the head; the other muscle 

 (ip) arises in the base of the prementum, and probably represents 

 the paraglossal muscle of other insects. The pull of these muscles 

 on the ends of the ligular supports (h) inflects the latter into the 

 membranous distal end of the prementum, and consequently retracts 

 the attached tongue, paraglossae, and salivary syringe, while the 

 subligular plate (k) is bent forward and upward beneath the base of 

 the tongue. 



The base of the retracted tongue (fig. 7 A, B), held by the pivotal 

 processes (i) of the ligular arms, is separated by a considerable 

 distance from the end of the subligular plate (k), to which the tongue 

 rod (rd) is affixed. As a consequence the rod has been drawn in a 

 wide loop far out of the base of the tongue. Since the rod traverses 



