58 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. yj 



Since the time of the earHer writers on the chordotonal organs — • 

 von Siebold, Leydig, Graber — our knowledge of these structures 

 has been greatly augmented through the work of many other in- 

 vestigators. Among the latter should be mentioned von Adelung 

 (1892), Herbig (1902), Janet (1904), Schwabe (1906), Berlese 

 (1909), Schon (1911), Vogel (1912), Lehr (1914), Erhardt (1916), 

 Hess (1917), Eggers (1920), and Mclndoo (1922); but the stu- 

 dent may obtain a complete list of papers on the chordotonal organs 

 from the bibliographical references in the works of these authors. 



Chordotonal organs are widely spread in insects, but they have 

 not been recorded in other members of the Arthropoda. In adult 

 insects they occur in the head, the thorax, the abdomen, the anten- 

 nae, the legs, and the wing bases ; in larvae they occur mostly along 

 the sides of the abdomen, but have been described also in the 

 labium, in the legs, and even in the tarsi. 



The characteristic chordotonal organs of larval insects are those 

 found in the abdomen, where a pair, one organ on each side, occurs 

 in each of the first seven or eight segments. Each organ is stretched 

 longitudinally between points on the anterior and the posterior 

 parts of the lateral wall of the segment, sometimes between infold- 

 ings of the cuticula (fig. 25), though usually no external characters 

 mark the site of the organ. The anterior attachment (c) is made by 

 the chordotonal ligament (d), the posterior one (^) by the ends 

 of the cap cells {^CCW). The chordotonal nerve {Nv') turns mesi- 

 ally from the sense cells (SCIs) to go to the ventral ganglion of the 

 segment. Organs of this type were described by Graber (1882) in 

 aquatic larvae of Coleoptera, in the caterpillars of Carpocapsa and 

 Tortix, in larvae of Diptera (Corcthra, Culex, Simuliiim, Ptychop- 

 tera, Tabanus), and in the larva of a sawfly (Nematus). Hess 

 (1917) gives a particular account of the chordotonal organs of 

 Cerambycid larvae, showing that the pleural discs along the sides 

 of these insects, on the first eight abdominal segments, mark the 

 points of their attachment, though the presence of chordotonal organs 

 within these discs was first noted by Schiodte (1869). 



In adult insects, the chordotonal organs are principally organs of 

 the legs and the wing bases, but they occur also in the head, the 

 antennae, the thorax, and the abdomen ; those connected with the 

 abdominal and leg tympana of Orthoptera are the best known. 



The so-called " ear " of the grasshopper, the tympanal chordo- 

 tonal organ located on the side of the first abdominal segment (fig. 

 27), is too well known to need a special description here. On the 

 inner surface of the tympanum (B, Tin) is a small cellular body 



