630 



ZOOLOGY 



SECT. 



with the nerves that end in it, constituting the retimda. Pigment 

 surrounds the crystalline cones and retinulse. 



The ocelli, or simple eyes (Fig. 535), consist of a biconvex 

 transparent thickening of the cuticle the lens and beneath it 

 of a group of specially modified epidermal cells. Some of these, 

 situated beneath the lens, form a transparent mass, the vitreous 

 body, another set of elongated cells being arranged to form the 

 retina. 



The antennae and palpi are the organs of touch, and these appen- 

 dages seem to be also the seat of the olfactory sense. A number of 

 minute processes sometimes sunk in pits, and each having a special 

 nerve-plate connected with it, are regarded as being specially con- 

 cerned with this sense ; and similar processes or pits on the maxillae 

 and the epipharynx are perhaps connected with the sense of taste. 

 The results of experiments on the action of the antennae seem to 



lead to the conclusion that 

 one of their main functions 

 is to act as organs for 

 regulating the equilibrium 

 of the body. 



Peculiar nerve-endings, 

 supposed to be auditory, 

 occur in various parts of 

 the body. These are dis- 

 tinguished as chordotonal 

 or tympanic, according to 



-re 



FlG. 535. Section through the ocellus of a young the nature of that part of 



Dytiscus larva, ct. cuticle: f /k, cells of the , , o-nnnrafiis w h i r h 



vitreous body ; luj, epidermis ; I, cuticular lens ; no, djJpcUdl/ 



optic nerve :" re, retinal cells ; st, rods. (From Lang, f lmc ti O llS bv 



after Grenadier.) * 



to 



n 

 , 



response o the sound- 

 vibrations. In the chordotonal organs this is a tense thin chord ; 

 in the tympanic a tense membrane or tympanum. The name of 

 Johnston's organs is given to auditory organs of a tympanic type 

 which occur in the second segment of the antennae in the majority 

 of insects. 



In certain Insects the Fireflies and Glow-worms, belonging to the 

 order Coleoptera occur luminous organs for the productioa of 

 light- 



Sounds are emitted by many Insects, and are produced by a 

 variety of different means. Often the sound is the result of the 

 rubbing together of opposed rough surfaces of the integument. 

 The chirp of the Grasshopper, for example, is produced by the 

 rubbing of the femur of the last pair of legs over a series of ridges 

 on the anterior wing, and that of the Locust by the rubbing against 

 one another of the roughened basal parts of the first pair of wings. 

 In other cases the sound results from the rapid vibratory move- 

 ment of the wings ; this is the case with the buzzing of many 



