THE INTERNAL ANA.TOMY OF INSECTS 147 



the cap-cell {c:), in which there is a nucleus {ecu); extending from 

 the end -knob (ek) of the scolopale and surrounded by the cap -cell 

 there is an attacliment fiber or terminal ligament {tl) , by which the 

 scolopophore is attached to the body-wall, the scolopophore repre- 

 sented being of the integumental type; at the base of the scolopale 

 and partly surrounding it, there is a vacuole (v) . 



The structure of a scolopale. — The scolopalas or auditory pegs are 

 exceedingly minute and are quite uniform in size, regardless of the size 

 of the insect in which they are ; but they vary in form in different 

 insects. They are hollow (Fig. 162,5); but the wall of the scolopale 

 is almost always thickened at its distal end, this forming an end-knob 

 (Fig. 162, ^^). They are traversed by the axis -fiber of the sense -cell. 

 The vacuole at the base of the scolopale connects with the limien of 

 the scolopale; this vacuole is filled with watery 

 fluid. 



In Figure 163 is shown a part of the scolopo- 

 phore represented in Figure 162, more enlarged 

 @(A), and three cross-sections (B, C, D) of the 

 '■ scolopale. The wall of the scolopale is composed 

 at either end of seven ribs (r), each of which is 

 -(.^ij.;- divided in the central portion, making fourteen 

 ^--— ^ ribs in this part. The entire scolopale, except 

 possibly the terminal ligament, is bathed in the 

 watery liquid, and is free to vibrate (Hess '17). 



Fig. i63.-Part of the j^ g^o^ld be remembered that the scolopate of 

 scolopophore shown . . . 



in Figure 162 more different insects vary greatly in form; the one 

 enlarged (From figu^j-ed here is merely given as an example of 

 one type. 



The simpler forms of chordotonal organs. — In the simplest form 

 of a chordotonal organ there is a single scolopophore; usually, how- 

 ever, there are two or more closely parallel scolopophores. In figure 

 164, which represents a chordotonal organ found in the next to the 

 last segment of the body of a larv^a of ChironomMS, these two types are 

 represented, one part of the organ being composed of a single scolopo- 

 phore, the other of several. 



The chordotonal ligament. — In Figure 164 the nerve connecting 

 the chordotonal organ with the central nervous system is represented 

 at n; and at U is shown a structure not yet mentioned, the chordo- 

 tonal ligament, which is found in many chordotonal organs. Figure 

 165 is a diagrammatic representation of the relations of the chordo- 

 tonal organs of a larva of Chironomus to the central nen.^ous system 



