Introduction to Animal Morphology. 389 



a ganglion whose nerves end in club-like rods, with 

 fine acoustic hairs. This is placed under the knee on 

 the outside of the front pair of legs in Crickets, or in a 

 shallow depression on the metathorax, close to base 

 •of the third pair of limbs, and receiving its nerve from 

 the third thoracic ganglion in Acrididse. In Locusts 

 it is placed on the front pair of legs, and there is an 

 opening into its cavity. At the base of the halteres 

 of Diptera and at the base of the hind wings of beetles 

 there are areas where the chitinous integument is 

 pierced abundantly by pore-canals, and beneath which 

 are clusters of rod-like nerve endings, like those in 

 •other auditory organs, but with no tympanic ring nor 

 membrane.* 



Eyes are absent in cave-dwellers, or those living 

 in dark places, but are usually two, compound, ses- 

 sile, lateral, with sometimes accessory cornea-bearing 

 ocelli, varying in number: this class of eyes, or none, 

 exist in larvae as a rule. The compound eyes consist 

 of2o-, 50-,40oo (House-fly), 28,000 (Dragon-fly), hexa- 

 gonal, rarely quadrate facets. The organ is stalked in 

 Chloeon, Diopsis (Dipteron), and some Strepsiptera 

 and Hemiptera, but the stalks are not movable. 



The muscles of insects are grouped into those with, and 

 those without, prolongations from the exoskeleton (tendon) 

 for their insertion ; the first group are either conical, with 

 a single, or pyramidal with a laminated tendon, penniform 

 or compound (arising by several heads). In the larva of 

 Cossus ligniperda there are 228 muscles in the head; 1647 

 in the body; and 21 18 in the viscera; but these, which 

 are little more than divided fasciculi of fibres, are capable 



* Hicks and Lespes describe auditory (?) vessels in the antennae of 

 Lamellicornes. 



