THYSANURA 



219 



ORDER THYSANURA* 



The Bristle-Tails 



The members of this order are wingless insects in which the wingless 

 condition is believed to he a primitive one, there being no indication that 

 they have descended from winged ancestors; the month-parts ore formed 

 for cheiving; and the adult insects resemble the young in form. In these 

 three respects, these insects resemble the next order, the Collembola; but 



they differ from the Collembola in 

 that the abdominal segments are 

 not reduced in number and the 

 cerci are usually filiform and 

 many-jointed; some members of 

 the order have also a caudal fila- 

 ment. 



The members of this order 

 are known as bristle-tails, a 

 name suggested by the pres- 

 ence, in most of them, of either 

 two or three many- jointed 

 filiform appendages at the cau- 

 dal end of the body (Fig. 221, 

 c, and m f) . 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. 

 In fdpyx (Fig. 222), the cerci 

 are not jointed but are strong, 

 curved appendages, resembling 

 the forceps of earwigs. 



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 fre- 

 quents warm ones, about fire- 

 places and in bakehouses. The 

 antennae are long and many- 

 jointed. In the Machilidas 



Fig. 221. — Machilis, ventral aspect: c, cer- 

 cus ; Ip, labial palpus ; mf, median caudal 

 filament: mp, maxillary palpus; 0, ovi- 

 positor; s, s, styli. 



"Thysanura: thysanos (Svpavos), a tassel; oiira {ovpd), the tail. 



