364 



THE ANATOMY OF INVERTEBRATED ANIMALS. 



thorax are hardly distinguishable, and the abdomen has nine 

 visible segments. 



Fig. 103.— Perla nigra— k. The aquatic apterous larva. B. One of the transitional 

 stages between this and the perfect insect, C. ( -t Kegne Animal. 1 ') 



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 Ortlioptera x (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 TJiysanoptera {Thrips 



1 The Thysanura and the PJn/snpoda are often united with the Ortlwptera 

 in modem classifications, while the Ephemerid<z and Libellulidce used to be 

 arranged with the JVeuroptera. 



