THE EYES. Xliii 



below the eyes, and on the inferior surface of the head : 

 therefore in these insects the ocelli do not look upwards. 

 The rostrum is short, and takes its rise at the base of 

 the clypeus, and is of variable length ; it is composed 

 of three joints, and is folded between the cox?e. The 

 short basal portion is often hidden behind the clypeus ; 

 the second and third joints are unequal in lengtli ; the 

 whole forms a sheath for the three lancet-like hairs 

 suited for sucking. Examples of these details may be 

 seen on Plate A, figs. 1, 2, 3. 



The Eyes. Oculi and Ocelli. Les Yeux. Augen. 



The Tettigidse are provided with both compound and 

 simple eyes. 



The oculi are generally reniform, two in number, 

 and placed right and left of the vertex. The ocelli, 

 if present, number two or three, and occur either on 

 the base or on the vertex of the crown, or else they are 

 placed below the insertions of the antennas. 



Larval forms often show these ocelli as mere 

 rudiments, and, indeed, in many images they are 

 represented only by pigmental spots. 



The ocellus has a convex transparent covering which 

 seems to fit into a kind of cavity in the integument. 

 But, according to J. Muller, there lies behind this a 

 true crystalline lens, larger than it, and which cor- 

 responds with the entire circumference of the eye (see 

 Burm. Handb. 293). The anterior surface of this lens- 

 like body has a curvature different from that of the 

 posterior ; its function, perhaps, is to correct spherical 

 aberration. The optic nerve spreads itself at the 

 posterior margin of the crystalline body, and has its 

 corresponding pigment-cells attached. According to 

 J. Muller a true iris lies behind this lens. The pigment 

 of the visual organs is of different colours, partly 

 dependent on the maturity of the insect, and partly on 

 the time which lapsed after the insect had undergone 

 its metamorphosis. 



