14 ILLINOIS BIOLOGICAL MONOGRAPHS [408 



central spindle ( Shelf ord 1915:243, Fig. 1). In the Cieindelidae the 

 chitinous columns are not arranged in any very definite manner but in 

 some cases they retain their pigment within areas that are not other- 

 wise pigmented. 



Hairs which in a primitive insect usually cover the wing entirely 

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

 representative of the Pogonostomidae, and one of the Megacephalidae, 

 Megacephala (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 euticula 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 euticula. Hairs occur in practically all groups, though 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 shown by small circles 

 in figures 2 to 29, plate I to III. 



The elytra of many species are marked with pits. 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 

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

 Horn has suggested. I have seen no pits that would appear to represent 

 rudimentary hairs though they may occur. 



There are sometimes thickenings running lengthwise of the elytron 

 as in Domica (Shelford, 1915: Figs. 35 and 36). While these thicken- 

 ings run parallel with the trachea, they are usually between rather 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 w r ay to veins (particularly in Mantichora). 

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

 resemble veins, almost invariably containing tracheae. The subcosta 

 usually follows the 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 chitinous 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 Mantichora there are distinct ridges 

 over them which have every appearance of veins. 



