Orthoptera, &c. — Hemiptera 349 



generalised and specialised characters are mixed in 

 all three. The wingless forms are clearly degraded. 

 The Termites, an ancient and well-defined family, 

 owe their survival to their adoption of the social habit. 

 The presence of long, jointed cercopods as the pre- 

 cursors of forceps in at least one species of Earwig 

 suggests a thysanuroid ancestor for the entire group. 

 Thysanoptera and Hemiptera. — The Thysanop- 

 tera which have been united by some authors with 

 the Platyptera, by others with the Hemiptera, are 

 clearly intermediate between the group which we have 

 just considered and the last-named order. Their small 

 size and the reduction or absence of wings stamps 

 them as a degraded order; but the structure of their 

 jaws marks a stage between the normal biting organs 

 of the Platyptera and the sucking and piercing mouth- 

 parts of a Bug ; the mandibles are converted into 

 stylets, though the maxillse retain their palps. The 

 Thysanoptera then may be regarded as a degraded 

 offshoot from the extinct ancestors of the Hemiptera, 

 these ancestors being themselves derived from primi- 

 tive mandibulate insects. Except for the connection 

 with the Thysanoptera just suggested the Hemiptera 

 are one of the most isolated of insect-orders ; with little 

 or no metamorphosis we find a high specialisation 

 of adult structure, with gi-eat variety and flexibility in 

 details so that the order contains many families and 

 multitudinous species. Not the mandibles only as in 

 the Thysanoptera, but the first maxillse also are 

 developed as stylets, while the second maxillse unite 

 to form a tube wherein these piercers work ; the palps, 

 almost always absent, remaining rarely in a vestigial 

 state. Associated with this specialised and character- 

 istic mouth is to be found the greatest variety in 

 form of body, development of wings, and habit. It 

 is of special interest to notice that those sub-orders 



