14 ILLISOIS BIOLOGICAL MOXOGRAPHS [408 



central spindle (Shelford 1915:243, Fig. 1). In the Ciciudelidae the 

 ehitinous columns are not arranged in any very defiiiite manner but in 

 some eases they retain their pigment within areas that are not othei-- 

 wise pigmented. 



Hairs which in a primitive insect usually cover the wing entirely 

 are present in nearly all tiger bettle elytra. In the ilautiehoras, observed 

 representative of the Pogonostomidae, and one of the Megacephalidae, 

 Mcgacephala {Tetracha) aequinoctialis, the elytra are more or less com- 

 pletely and uniformly covered with small hairs. Under the microscope 

 the hairs may be located on the pigmented area of the elytra by the 

 light area which is produced by the thin cuticula at the base of each 

 hair. Hairs appear on the whole to be less common in the unpigmented 

 areas and when present usually are surrounded by a narrow rim of 

 pigmented cuticula. Hairs occur in i^ractically all groups, thoiigli they 

 have been lost from the majority except for a few at the base of the 

 elytron and scattered along the tracheae ( Shelf ord, 1915:243, Figs. 

 1 to 3). These are present in Cicindela and are sho's\ai by small circles 

 in figures 2 to 29, plate I to III. 



The elj'tra of many species are marked with jjits. Close examin- 

 ation under the microscope with both transmitted and reflected light 

 shows that, in the majority of cases, the pits are over the center of the 

 ehitinous columns and bear no relation to rudimentary hairs as Dr. W. 

 Horn has suggested. I have seen uo pits that would appear to represent 

 rudimentary liairs though they may occur. 



There are sometimes thickenings running lengthwise of the elytron 

 as iu Domiea (Shelf ord, 1915: Figs. 35 and 36). While these thicken- 

 ings run parallel with the trachea, they are usually between ratlier than 

 coincident with them, except in Caledonica (Fig. 25). There are, how- 

 ever, some thickenings on the under side of the elytra of most species 

 which correspond in a general way to veins (particularly in Mantichoi'a ) . 

 The outer and inner margins of the elytra are always thickened and 

 resemble veins, almost invariabl.y containing tracheae. The subcosta 

 usually follows tlie costa very closely at the base of the elytron but just 

 behind the middle it turns inward away from the margin in a vein like 

 thickening. The radius is in a distinct thickening of the elytron which 

 proceeds from the base for a short distance. This is very constantly 

 present. Aside from this nothing comparable to veins is present but the 

 rows of ehitinous columns are often so arranged so as to give distinct 

 and direct spaces running the length of wing. These are occupied by 

 the principal tracheae. In some cases the spaces appear very clearly on 

 the under side of the elytron and in JMautichora there are distinct ridges 

 over them which have every appearance of veins. 



