LYSECTA. 19 



The organs of sense are directly connected with the 

 head or its appendages, except the '• tympanal organs," 

 and these may be taken up in connection with the ab- 

 domen. They are light-colored, oval membranes, one 

 on either side of the first abdominal ring, and are sup- 

 posed by many to be organs of hearing. They are 

 modified portions of the two layers of the skin. On 

 the inner side they are connected with rod-bearing 

 organs, which in turn lead to a ganglion, and from the 

 latter a nerve passes to the third thoracic ganglion,^ 

 and thence to the brain. It is supposed by those 

 who hold that these organs are ears that when a wave 

 of sound strikes the tympanum, the vibrations affect 

 the rod-bearing organs, and are transmitted to the 

 thoracic ganglion, and thence forward to the brain. 



Before taking up the appendages, the compound 

 eyes (PI. I., Fig. 4, ey) must be considered. It may 

 seem more natural to describe these organs when 

 observing the structure of the head (see p. 13). They 

 are considered here in order to treat of the sense 

 organs together, and also because there seems to be a 

 connection, not yet well understood, between the eyes 

 and antennae, those insects with small eyes having 

 very often well-developed antennae, and vice ve^sa. 

 There are, however, numerous striking exceptions to 

 this rule. The eyes project on either side, and are 

 fixed or sessile. In some insects, like Stylops (Fig. 



1 See Minot, " Comparative Morphology of the Ear," Amei'- 

 ican Jow-tial of Otology, Vol. IV., April, 1882. The author 

 considers that the " tympanal organs " are unquestionable sense 

 organs, although in his opinion the evidence is decisive against 

 the supposition that they are ears. 



