68 Annals Entomological Society of America [Vol. X, 



inous invagination, at both the posterio-dorsal and anterio- 

 ventral ends, as shown in Figs. 2 and 4 (C. Inv.). Instead of 

 opening directly laterally, the pockets open at an angle of 

 about 45 degrees directed away from the pleural tubercle. 



THE CHORDOTONAL ORGAN. 



On examining the larvae internally, one finds in the case of 

 the Prionids with the pleural discs, that a peculiar structure in 

 the form of a chordotonal ligament is attached at the central 

 point of the disc, and stretched in an anterio-ventral direction 

 across an irregularly shaped enlargement on the pleural zone, 

 and attached at the other end to a fold in the body wall, as is 

 shown in Fig. 5 (Ch. L.). This ligament is very slender for its 

 posterior two-thirds, but soon thickens towards its anterior 

 third, to two or three times the size of the posterior portion. At 

 about one-half the distance between the beginning of this 

 swelling and the anterior attachment, a branch of the first 

 nerve of the corresponding segment enters the structure from 

 the side. This is the chordotonal nerve (Ch. N.). Anterior to 

 the entrance of the nerve, the structure narrows slightly until 

 it attaches. In the case of the organs in the seventh and eighth 

 abdominal segments, the condition is slightly different in that 

 the anterior attachment is at the anterio-ventral end of the 

 pleural tubercle, instead of on an anterior body fold as in the 

 other six pairs. This latter condition exists in all eight of the 

 abdominal segments of such species as Saperda Candida, Rha- 

 gium lineatum, and Desmocerus palliatus. The fact that the 

 ligament attaches anteriorly at the anterio-ventral portion of 

 the pleural tubercle often causes a faint external evidence of a 

 pleural disc in this region. 



In Monohammus confusor, the condition is much the same 

 except that at each end of the pleural tubercle, there is a large 

 chitinous invagination (Figs. 2 and 4, C. Inv.) which projects 

 into the body for a short distance. A chordotonal ligament 

 similar to the one described above, is stretched across the ends 

 of these chitinous structures (Fig. 6, Ch. L.). 



