THE INTERNAL ANATOMY OF INSECTS 147 



the cap -cell (cc), in which there is a nucleus (ccn}\ extending from 

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

 there is an attachment 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, s) ; but the wall of the scolopale 

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

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

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

 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). 



Jt should be remembered that the scolopate of 

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

 enlarged (From fig ure d nere j s 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 nex*t to the 

 last segment of the body of a larva of Chironomus, 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 li 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 nervous system 



