120 AN INTRODUCTION TO ENTOMOLOGY. 



from the simple form seen in the females. In Fig. 107, </ represents 

 the tegmina of a male Gryllits. It will be seen that the large veins 

 divide the wing into disk-like membranous spaces. If the principal 

 vein, which extends diagonally across the base of the wing. In 

 amined with a microscope, it will U Btt n to be furnished with 

 transverse ridges like a file t Fig. 107, b}. On the inner margin of the 

 wing, a short distance towards the base from the end of the principal 

 vein, there is a hardened portion which may be called the scraper. 

 This is shown enlarged at c in the figure. Each tegmina is therefore 

 provided with a file and scraper. When the cricket wishes to make 

 his call, he elevates his tegmina at an angle of about forty-five de- 

 grees with the body ; then holding them in such a position that the 

 scraper of one rests upon the file of the other, he moves the tegmina 

 back and forth laterally, so that the file and scraper rasp upon each 

 other. This throws the tegmina into vibration, and produces the call. 

 The Gryllidae is a comparatively small family, but the American 

 species have not yet been monographed. The few genera which I 

 have selected as illustrations, and which are our most common ones, 

 can be separated by the following table : 



A. Fore tibiae broad, fitted for digging. (Fossorial Crickets.) 



B. Insect small ; antennae ten- to twelve-jointed. i. TRIDACTYLUS. 



BB. Insect large; antennae many-jointed. 2. GRYLLOTAIPA. 



AA. Fore tibiae slender. 



B. Hind femora stoutish. (True Crickets.) 



C. Last segment of the maxillary palpi of the same length as the next 



to the last. 3. GRYLLUS. 



CC. Last segment of the maxillary palpi double the length of the next to 



the hist. 4. NKMOBIUS. 



BB.Hind femora slender. (Tree-crickets.) 5. CEi AN mrs. 



The Fossorial Crickets. We have two genera representing this 

 group ; they are commonly known as Mole-crickets. There are 

 species belonging to the next group, the true crickets, which burrow 

 in the ground ; but the mole-crickets, as their common name indi- 

 cates, are pre-eminently burrowers. The form of the body is that 

 suited to this mode of life. The front tibiae, especially, are fitted for 

 digging. They an- greatly broadened, and shaped somewhat like a 

 hand, or the feet of a mole. Gryllotalpa is the better known of 

 these two genera, this is doubtless owing to the large si/.e of tin 



. The Northern Mole-cricket, Gryllotalpa bored/is, inhabits nearly 

 the whole of the United States east of the great plains, from Lou- 



na to Massachusetts. It is not a common insect, but occasion- 

 ally it is found in great numbers in a limited locality. It can be 



