140 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 81 



the anterior wall of the labium, apparently, is united also the hypo- 

 pharynx (fig. 54 D, Hphy), and the duct of the silk gland opens 

 through a hollow spine, the spinneret, at the tip of the labium. 



Each maxilla includes a cardinal area (fig. 53 A, Cd), a stipital 

 area {St), both united with the basal part of the labium, and a free 

 terminal lobe {Lc) , which appears to be the lacinia. A maxillary palpus 

 is lacking. The area of the cardo- includes one principal sclerite (fig. 

 53 A, B, E, F, Cd), and generally one or two accessory plates (A, E, 

 F, k, k). The principal sclerite is always articulated to the hypostomal 

 margin at a point (c) corresponding with the articulation of the cardo 

 to the cranium in orthopteroid insects. The area of the stipes (St) 

 is variously chitinized, or unchitinized, but it always preserves the 

 ridge (q) of its inner margin, upon which are attached all the stipital 

 muscles. The homology of the terminal lobe of the maxilla is difficult 

 to determine. 



The musculature of the maxilla of a caterpillar comprises muscles 

 pertaining to its three parts, most of which are comparable to the 

 maxillary muscles of the grasshopper or other generalized insects, 

 though there is little similarity in the general appearance of the struc- 

 ture in the two cases. The cardo, in the caterpillar, is provided with 

 two or three muscles (fig. 53 B, E, F. 6, 7, 8), all of which arise on 

 the anterior arm of the tentorium (D, E), and, therefore, represent 

 the tentorial adductors of the cardo in orthopteroid insects. The usual 

 cranial muscle of the cardo (fig. 25, /, fig. 40 C, 10) is lacking in the 

 caterpillar. The stipes is provided likewise with tentorial adductors 

 (fig. 53 B, D, E, F, g, 10, 11) inserted on its mesal chitinous ridge {q). 

 The terminal maxillary lobe is moved by muscles that arise within the 

 stipes (B, F, 12, jj), and also by a long muscle (B, 14) having its 

 origin in the posterior angle of the hypostomal plate (Hst) of the 

 epicranium. These three muscles are inserted upon a basal sclerite 

 in the ventral wall of the maxillary lobe (A, B, /). The first two 

 suggest the ordinary stipital muscles of the lacinia, but the third (14) 

 appears to have no homologue in more generalized insects, since the 

 usual cranial flexor of the lacinia (fig. 30 B, ficc) is inserted on the 

 median angle of the latter. The insertion of the three muscles on a 

 single sclerite in the base of the maxillary lobe leaves no evidence to 

 indicate the presence of a galea, and suggests that the lobe is the lacinia 

 alone, complicated in form by the development of large sensory 

 papillae. Certainly, the musculature of the lobe shows that none of 

 the papillae can be a palpal rudiment. 



