THYSANURA. 55 



figure the mandibles are represented by a continuous line, and the 

 maxillae by a dotted one. It will be observed that only the tips of 

 these organs project from the cavity of the head. 



There are, as pointed out by Meinert and by Lubbock, among the Hexapods 

 three principal forms of mouth : 



" First, the mandibulate, in which the mandibles and maxillae are attached 

 externally, and are more or less powerful and adapted for biting and chewing. 



" Second, the suctorial, in which the mandibles and maxillae are attached 

 internally, and are not opposite, but parallel, and intended for pricking. 



"Third, the type presented by the Thysanura, in which the mandibles and 

 maxillae are attached internally, and are far from strong, but still have some 

 freedom of motion, and can be used for biting and chewing soft substances. 



The Thysanura includes three sub-orders ; these can be separated 

 by the following table : 



A. With well-developed abdominal legs, insect resembling a Myriapod in 

 form. I. SYMPHYLA. 



AA. With only six well-developed legs, 



B. Without ventral abdominal sucker. Caudal appendages bristle-like and 

 many-jointed, or in the form of a pair of forceps. II. CINURA. 



BB. With a bifurcated sucker or tubercle on the ventral aspect of the first 

 abdominal segment. Abdomen with a springing apparatus, or without ap- 

 pendages. HI. COLLEMBOLA. 



Sub-Order I. SYMPHYLA.* 



This sub-order has been erected for the reception of a single 

 genus, Scolopendrella. This genus includes certain minute insects 

 the zoological position of which is in doubt. All of the known species 

 are less than 7 mm. (.28 in.) in length. The general form of the 

 body resembles that of a Centipede ; and as with the centipedes, 

 each abdominal segment bears a pair of legs. But except in the 

 presence of these abdominal legs the structure of the body is more 

 like that of the Cinura than that of the Myriapods. And the legs 

 are five-jointed and end in two claws as in the Cinura ; while in the 

 Myriapoda there are six joints, and always a single large claw. 



Sub-Order II. ClNURA.f 

 (Bristle-tails and Fish-moths^) 



Among the pests that annoy the housekeeper there is one which 

 is wingless, but can run rapidly, and which has long thread-like ap- 



* Symphyla: syn (<rvv), together; phyla (<f>vkrf), tribe, 

 f Cindra: cineo (^iveao), to move; oura (ovpd), a tail. 



