( I ISSH !< \ 1 



Kphrmrrida ;in.l ( )< l< >na 1 ;i . < )! v the 



^enrrali/rd order; though Kphrmrrida li;i very 



primitive Structures, notably the paired L'< nital open! 1 ducts. 



It is often statf(l th;it I'leroph-ra are t i primitive of winged 



insects. A. online to tin- view, thru. Ortlmptrni i. 

 the plrroptrran stem. They show. howr\rr. no evidi 

 Ancestry; and everything indicate^ that terrestrial 

 aquatic. Doubtless plcropteroid and ort hoj)teroid ii: <>th arose 



from a type that was winded, with many wint^ vein-, mandibulate. and 

 terrestrial a form like a thysanuran but with wi 



On the basis of metamorphosis, Plecoptera, Kphrmrrida and Odo- 

 nata form a natural group, Hemimetabola, in which the changes in 

 form during development are greater than in other Heterometabola, 

 the aquatic nymphs of these three orders being termed naiads by 

 Comstock. 



Odonata are naturally placed next to Ephemerida but are strongly 

 aberrant forms with a unique kind of specialization. 



Thysanoptera form a distinct order which is usually placed next to 

 Hemiptera, chiefly on account of the suctorial mouth parts, though 

 even in this respect there is no close agreement between the two orders. 

 They are aberrant and hard to place. Borner and Crampton find 

 resemblances between Thysanoptera and Corrodentia. 



Hemiptera form a homogeneous and monophyletic order, charac- 

 terized by the unique shape and arrangement of the mouth parts, 

 which are always of the same type (Muir). Hemiptera are somewhat 

 like Orthoptera and possibly originated with Thysanoptera from some 

 mandibulate and winged form. The conversion of mandibulate into 

 suctorial organs may be seen within the order Collembola, though it is 

 improbable that Hemiptera arose from forms like Collembola. Hemip- 

 tera are exceptional among insects with a direct metamorphosis in 

 their highly developed type of suctorial mouth parts. Homoptera 

 are on the whole more primitive than Heteroptera. 



Parasita, long a suborder of Hemiptera, should rank as an order, 

 apparently; though opinions differ in regard to this. 



In the early days of the classification, the sucking lice and the bitinir 

 lice were always grouped together, on account of their resemblance -. 

 Then it was found that these similarities, correlated with parasitic 

 existence, were only superficial; and the two groups were separated. 

 Some recent authors have, however, followed one another in the opinion 

 that the two kinds of lice are closely related to each other an opinion 



