364 THE ANATOMY OF INVERTEBRATED ANIMALS. 



thorax are hardly distinguishable, and the abdomen has nine 

 visible segments. 



FIG. 103. Perla nigra.K. The a 



One of the transitional 



Perla nigra.A. The aquatic apterous larva. B. One of the trail 

 stages between this and the perfect insect, C. (" Regne Animal.") 



The Orthoptera (Fig. 103) and the Hemiptera (Fig. 104) 

 are ametabolous. The majority have two pairs of similar or 

 more or less dissimilar wings in the adult state, and in the 

 apterous forms it is probable that the wings are aborted, not 

 typically absent. In the Orthoptera 1 (the Termites, Cock- 

 roaches, Grasshoppers, Crickets, Day-flies, Dragon-flies, and 



FIG. 104. Aphis pelargonii. Apterous agamogenetic form. 



Earwigs) the mouth is constructed upon the same plan as 

 that of Blatta ; but the Physopoda or Thysanoptera (Thrips 



1 The Thysanura and the Physopoda are often united with the Orthoptera 

 in modern classifications, while the JSphemeridce and Libellulidce used to be 

 arranged with the N6uroptera. 



