472 



COMPARATIVE ANATOMY 



CHAP. 



great, the terminal tubes are generally isolated, running either irregu- 

 larly or radially, or in the shape of a fan, etc., to the integument. 

 These peculiar sensory organs are called ehordotonal organs, and 

 are considered to be auditory. A ehordotonal organ may be either 

 simply connected Avith the integument by a prolongation of its nerve, 

 or bent at right angles to its nerve and run parallel to the integument 

 (Fig. 330). The latter is the case when the terminal tubes of the 



FIG. 330. Eight half of the 8th trunk segment of an older larva of Corethra plumicornis ; 

 nervous system and sensory organs (after v. Graber). g, Ganglion of the ventral chord ; Im, longi- 

 tudinal muscles ; en, ehordotonal nerve ; cl, ehordotonal ligament ; eg, ehordotonal ganglion ; os, rod 

 of the ehordotonal organ ; cst, terminal strand ; fb, tactile setK ; hn, outgoing fibres of the integu- 

 mental nerves. 



ehordotonal organ unite into one tube, and then the bent portion is 

 connected with the integument by a second tube, the ehordotonal 

 ligament. The ehordotonal organ, together with the ehordotonal 

 ligament, then form a chord stretched between two parts of one and 

 the same segment. 



The nerve forms a terminal ganglion cell at the point where it joins 

 the chord. 



If the exoskeleton is affected by vibrations of sound, this apparatus 

 with its terminal rods is set in vibration, and a sensation of sound may 

 thus be produced. 



Chordotonal organs, which offer great varieties of structure, occur in all orders 

 of the Ptcrygota, and are found in the most various parts of the body, in the trunk, 

 in the legs, the wings, the mouth parts, and the antennae. They may appear in 

 different forms in various parts of the body of the same animal. 



