XI 



PHYLUM ARTHROPODA 



645 



-re 



FIG. 524. Section through the ocellus of a young 

 Dytiscns larva, ct. cuticle : gk, cells of the vitreous 

 body ; hy, epidermis ; I, cuticular lens ; no, optic 

 nerve : re, retinal cells ; st, rods. (From Lang, after 

 Grenacher.) 



The ocelli, or simple eyes (Fig. 524), consist of a bi-convex 

 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 appendages 

 seem to be also the seat 

 of the olfactory sense. A 

 number of minute pro- 

 cesses sometimes sunk 

 in pits, and each having a 

 special nerve-plate con- 

 nected with it, are regarded as being specially concerned 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 regulat- 

 ing the equilibrium of the 

 body. 



Peculiar nerve-endings, 

 supposed to be auditory, 

 have been found in various 

 parts of the body. Each 

 consists of a ganglion-cell 

 (Fig. 525, #z.) giving off a 

 process which is enclosed 

 in an elongated tube, and 

 which ends externally in a 

 slender rod (sc.). Groups 

 of these are associated to- 

 gether to form the auditory 

 organ. 



In certain Insects the 

 Fireflies and Glowworms, 

 belonging to the order Col- 

 eoptera, occur luminous organs for the production 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 

 nibbing together of opposed rough surfaces of the integument. 

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



FIG. 525. Chordotonal (auditory) organ in the tibia 

 of Isopteryx apicalis. bk, blood-corpuscles ; 

 c. integument ; es, terminal fibrous strands at- 

 tached to the integument ; (jz, nerve-cells : c. ter- 

 minal rods ; tr. trachea. (From Lang, after v. 

 Graber.) 



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