138 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8l 



situated on membranous areas just laterad of the bases of the man- 

 dibles, while the antennae of the adult arise from the facial region 

 above the compound eyes. The ventro-lateral position of the larval 

 antennae, therefore, appears to be a primitive character in the cater- 

 pillars. 



Each antenna of the caterpillar consists of three segments, of which 

 the middle one is usually the largest, the proximal segment being 

 often reduced to a mere basal ring (fig. 51 E, Ant), and the terminal 

 one appearing as a minute apical papilla of the second. The mem- 

 lirane of the antennal base may form a large mound with the antenna 

 retractile into it, or sometimes a long cylindrical projection simulat- 

 ing a basal segment (fig. 50 C). A hypodermal fold projects inward 

 from the base of the antenna (fig. 50 D) which receives the antennal 

 nerve and trachea. Each antenna is moved by a single set of muscle 

 fibers, which are : 



J. — TJie retractor muscles of the antenna (fig. 50 B — F). — -A group 

 of slender fibers arising on the parietal walls of the cranium laterad 

 of adf rontal area ; inserted on anterior inner angle of base of proximal 

 antennal segment. Extension of the antennae is probably effected by 

 blood pressure from within the head. 



THE MANDIBLES 



The mandibles of the caterpillar are typical insect jaws suspended 

 from the lower margins of the cranium by a hinge line sloping down- 

 ward posteriorly, with well-developed anterior and posterior articula- 

 tions. The anterior articulation of each mandible consists of a condyle 

 on the cranial margin placed just laterad of the clypeus (fig. 52 A, c), 

 received into a socket on the base of the jaw ; the posterior articulation 

 (a) is the reverse, consisting of a socket on the cranial margin receiv- 

 ing a condyle of the mandible. As in all insects, the articular points 

 of the jaw lie outside the membrane that connects the base of the 

 mandible with the head. A line between the two articulations divides 

 the base of the jaw unequally (fig. 52 B), the larger part being mesad 

 to the axis. 



The muscles of the mandibles are inserted on large but weakly 

 chitinized apodemal inflections arising at the outer and inner margins 

 of each jaw. The muscles take their origin on the walls of the cranium 

 and on the ventral apodemes of the postoccipital ridge. Their fibers 

 occupy most of the cavity of the head, and the cranial hemispheres 

 appear to model their form on that of the bases of the great adductor 

 muscles of the jaws. 



