CHAPTER III 

 ORDER THYSANURA* 



The Bristle-tails 



The members of this order are wingless insects still in a primitive con- 

 dition. The mouth-parts are formed for chewing and the adults resemble the 

 young in form for they do not have marked metamorphosis. The segments 

 of the abdomen are of the usual number, eleven, and the last one usually 

 bears two or three long, segmented, filiform appendages. 



The members of this order are known as bristle-tails, a name sug- 

 gested by the presence, in most of them, of either two 

 or three many-jointed filiform appendages at the caudal 

 end of the body (Fig. 74) . The paired caudal appendages 

 are the cerci; the median one, when three are present, 

 is the median caudal filament, a prolongation of the 

 eleventh abdominal segment. 



The bristle-tails are most often found under stones 

 and other objects lying on the ground ; but some species 

 live in houses. While most species prefer cool situations, 

 there is one, the fire-brat, that frequents warm ones, 

 about fire-places and in bakehouses. The antennas are 

 long and many-segmented. There are less than twenty 

 species known in this country. 



In one family the compound eyes are very perfect 

 but in all others they are more or less degenerate or are 

 lost entirely. 



The mouth-parts are formed for chewing but in 

 many of the forms the jaws are apparently sunk in the 

 head due to being overgrown by folds of the cheeks, or 

 ■ genas. In two families the jaws are not overgrown and 

 the mouth-parts project in a normal manner. 

 An interesting feature of some members of this order is the short, 

 slender, two-segmented appendages found on the ventral side of the 

 abdomen and known as styli. The styli are believed to be vestiges of 

 legs persisting from many-legged ancestors probably centipede-like 

 animals, the symphylids (See, An Introduction to Entomology, p. 23.) 



A common representative of this order is the fish-moth or silver-fish 

 (Lepisma saccharina) as it is variously called. 



Often the careful housekeeper sees in the ironing-basket, or upon the 

 book-shelf where she is dusting, a flash of light like a tiny thread of quick- 

 silver, that usually vanishes as soon as seen. 



If she is experienced she knows that this streak of light is a little 

 animal, half an inch long, whose body is clothed in shining scales like 

 * Thysanura: thysanos (dOa-avos), a tassel; our a, (ovpa), the tail. 



45 



— Lepisma 



