10 INTEODUCTION. 



Determination of Species. 



In attempting to determine the species of an earwig, until 

 experience has taught the distinction of the leading groups, the 

 Table of Families on p, 31 should first be consulted. The species 

 of the ApacJiyidie are so distinctive and so few in number, that 

 thej can be recognized almost at a glance. If the specimen is not 

 one of the Apacliyida'., the femora should be examined ; if these 

 are compressed and have one or two little ridges running down 

 them, the specimen is one of the Pyg idler ani dee. The appearance 

 of the two subfamilies of this group are quite distinctive. Each 

 subfamily has its own strong family likeness, but although it is 

 easy to recognize a member of the Dlplatyince or Pyr/idicranince at 

 a glance, it is usually a matter of some difficulty to determine the 

 species. If the femora are smooth, the tarsi should be examined; 

 if the small second segment has any lobe or dilation, the specimen 

 is one of the Forficulidce, and if not, it must be referred to the 

 Labidurimc or to the Lahiida;. In the fox'mer family, the dorsal 

 surface of the last segment is folded downward between the base 

 of the forceps and so presents a vertical face, which sometimes is 

 separated from the dorsal horizontal face by an angle, but the 

 passage is often gradual. In the Lahiidiv, this does not occur, 

 there being an opening between the roots of the forceps and the 

 dorsal and ventral plates of the end of the abdomen, and in this 

 space there may often be seen the chitinous organ of diversified 

 shape termed the i^ygldium. It is worth while giving an 

 imaginary example of these synoptical tables. 



The examination of our undetermined earwig perhaps shows a 

 small lobe on the second segment of the tarsi ; we accordingly 

 turn to the Table of the Subfamilies of the Forjtculido} on p. 129. 

 We again examine the second tarsal segment and observe that it 

 is broadened out on each side, thus assuming a heart-shaped out- 

 line ; this precludes the ChelisocMno'. Next, turning the speci- 

 men over and examining the sternal plates, we find that these 

 are not decidedly broader than they are long, which precludes 

 the Anechuriiue. The body is rather depressed — somewhat 

 widened about the middle ; a cross-section would not be circular, 

 but would show a depressed transverse ellipse. Therefore it must 

 be referable to the Forficulince, and we turn to the Table of Genera 

 on p. 162. 



The shape of the forceps, which are very broad and flat near the 

 base, but become suddenly elongate, arcuate and slender, show 

 that it is a Forficula, and we turn to the Table of Species on p. 165 

 "We see that the pronotum is not very decidedly transverse, so 

 this precludes the first four species. Neither is it crescent-shaped, 

 and this precludes the next two. As the dilation of the forceps is 

 not confined to the extreme base, but extends about a quarter or 

 a third of the length of these organs, it cannot be F. ambigna. 

 The elytra and wings are not spotted, so it cannot be F. lucasi. 



