ANTENNATA SENSORY ORGANS 



473 



In the wings, but especially in the halteres or balancers of the Diptera, which are 

 minute transformed hind wings, they are connected with areas of the exoskeleton 

 provided with peculiar pores or papillre. They always lie superficially. A chordo- 

 tonal organ is, further, never stretched between points of the integument of two con- 



FIG. 331. The Chordotonal 

 organ of Fig. 330, strongly mag- 

 nified, el, Chordotonal ligament ; 

 en, chordotonal nerve ; eg, chord- 

 otonal ganglion ; cst, chordotonal 

 rod ; es, terminal tube. 



FIG. 332. So-called sub-genual Chordotonal organ 

 in the tibia of the middle leg of Isopteryx apicalis 

 (Perlid) (after v. Graber). tr, Trachea; bk, blood 

 corpuscles ; gz, nerve cells ; sc, scolopophores with 

 their rods ; es, terminal fibrous strands, attached to the 

 integument (c). 



secutive segments of the body, or limbs, movable on one another, but always runs 



within one of the same joint or segment, and is thus not affected by the movements 



of the animal. The chordotonal nerves always arise out of the 



ganglion belonging to their own segment. Chordotonal sensory 



organs have till now been chiefly observed in the larvae of the 



Insecta. 



The tympanal organs of the Saltatoria, which have been long 

 known, agree in the finer structure of their nerve endings with 

 the chordotonal organs. It was this agreement which led to the 

 assumption that the so-called chordotonal organs were also 

 auditory organs, for the tympanal organs of the Saltatoria have 

 long been universally regarded as auditory organs, although the 

 animals continue to hear after their removal. This last fact 

 favoured the view of the acoustic properties of the chordotonal 

 organs, since the latter occur together with the tympanal organs. 



Scolopophores are very numerous in the Saltatoria (over 100). 

 In the Acridiidce their terminal tubes are attached to points of 

 the inner surfaces of the hypodermis of special parts of the 

 exoskeleton, which, as compared with the surrounding exoskeleton, 

 are thinned away like a membrane and are called tympana 

 (Figs. 333 and 334). Such a tympanum may be stretched between 

 thickened portions of the skeleton, which form a frame for it ; 

 and, as in an outer ear, the integument may grow round it as a 

 covering fold for its protection. A tracheal trunk widens to form a cavity under the 

 tympanum, which may be compared with the hollow of a drum. Between the cavity 



FIG. 333. Tibia 

 of the fore leg of 

 Locusta viridis- 

 sima. td, Cover of 

 the drum ; tr, fissure 

 between the drum 

 and its cover (after 

 v. Graber). 



