AUDITORY TISSUES 



217 



hairs of many arthropods, and also closely resembles the static hairs of 

 the shrimp, which we have studied, thus showing the close relationship 

 that exists between these 

 three forms of sense organs 



(Fig. 195). 



The chordotonal organs 

 in the limbs of some katy- 

 dids represent another differ- 

 ent and somewhat more 

 specialized form of auditory 

 apparatus. It is a wonderful 

 organ because of the many 

 kinds of highly differentiated 

 tissues that cooperate to form 

 it. A very large trachea , 



J vi 11- FIG. 195. Longitudinal section of second antennalseg- 



COmCS into the limb and lies ment of a. mosquito, MocMonyxculiciformis. aud.or., 

 in Very close Contact with One auditory organ. (After CHILD in Zeitschrijt f. wiss. 



side of it. The outer cuticle 



of the limb becomes thin on an oval area of this contact, and this area 

 forms the tympanum of the auditory organ. The tympanum is thus 

 made of two thin layers of cuticle (for the trachea is a portion of invagi- 

 nated integument) between which lie the two layers of simple epithe- 

 lium which have formed them. 



In the anterior of the two widening spaces, where these two walls of 



the tympanum sepa- 

 rate, lie the auditory, 

 perceptory cells (Fig. 

 196). They are of 

 two kinds, in which 

 the differences are 

 sen.c. mostly those of size 

 and general form. It 

 is also possible, if 

 these perceptory cells 

 were derived from the 

 ectodermal tissues, as 

 they probably were, 

 that the cells of one 

 group originated from 

 the tracheal epithe- 

 lium, while the others 

 came from that of the outer integument of the limb. These cells are 

 connected with some central ganglion by two nerves that unite upon 



--sen c. or. 



FIG. 196. Part of a longitudinal, vertical section of the fore 

 tibia of a young katydid, Microcentrum laurifolium, 10 mm. 

 long. Chordotonal organ, sen.c., sensory cells; sen.c.or., cell- 

 organ of sound perception; cu., cuticle of trachea. X 1200. 



