TYPE TRACES AT A. 505 



on the other hand, membranous and the veins are for the 

 most part arranged longitudinally, so that when at rest the 

 wings are folded like a fan, though in some forms, such as 

 the Crickets, in which the anterior wings are short, a trans- 

 verse fold also occurs. In the female Cockroaches the ante- 

 rior wings are very small, and the posterior ones wanting, and 

 in the Walking Stick (Diapheromera) so named from its resem- 

 blance to a green or dead twig both pairs are entirely want- 

 ing. 



The antenDse are usually long and filiform, and the legs 

 strong and adapted to a terrestrial life, some forms, such as 

 the Cockroach, being exceedingly active. In the Grasshop- 

 pers, Locusts, and Crickets the femora of the last pair of legs 

 are greatly enlarged and very muscular, serving for jumping, 

 while in the Mole-cricket (Gryllotalpa), which burrows in the 

 ground, the anterior pair is greatly enlarged and adapted for 

 digging. 



As in the Earwigs, the metamorphosis is gradual. 



3. Order Ephemeridae. 



The Ephemeridse, or May-flies (Fig. 234), are characterized 

 by the remarkable brevity of their existence in the imago- 

 stage, some forms existing but for a few 

 hours, while others live for several days, 

 the existence being merely long enough 

 to ensure the accomplishment of the re- 

 productive acts. The body is elongated 

 and terminates in two or three elongated 

 hairlike cerci, and on the thorax there are 

 borne usually two pairs of wings, of which 

 the anterior pair is considerably larger FIG. 231.Potamanthus 

 than the posterior. The antennae are marginatus (from PACK- 

 short, and the mouth-parts adapted for 



biting, though usually much reduced, since the imago takes 

 no nutrition during its short existence. The first pair of legs 

 is usually slender and directed forwards, being of little use in 

 locomotion. An interesting structural peculiarity is the oc- 

 currence of paired reproductive ducts which open by separate 



