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THE AMERICAN NATURALIST 



[Vol. UII 



sects, and they appear to have departed as little as any 

 from the ancestral condition of these groups, so that they 

 are as important as any synthetic types, with the possible 

 exception of the Palaeodictyoptera, for a phylogenetic of 

 winged insects in general. The great antiquity of fossil 

 Plecoptera is also in harmony with the idea that the 

 Plecoptera are quite like the ancestors of the higher 

 forms, and since the anatomical and phylogenetic data 

 are in complete harmony in this respect, we are justified 

 in assuming that the Plecoptera have departed as little 

 as any forms from the ancestral condition of the groups 

 next to be considered. 



The Plecoptera, embiids, and Dermaptera originated 

 from essentially similar ancestors, which were not far 

 removed from present-day Plecoptera, and their lines of 

 descent have followed a common developmental road for 

 a considerable distance, before first the embiids, and a 

 little later the Dermaptera branched off to follow their 

 own paths of specialization (Crampton, 1917a). The 

 IIcniinicn(s-]\ke forms branched off from the Dermapteron 

 >tocl< at ail viivW date, and a little later, the Coleopteron 

 Ixfi' \\a- (litTciTmi.-itra. T\n^ Strci)>iptera were possibly 

 .lilh-nMitialcd IV.mii ;i Hinilar >l(U'k still later. The terms 

 "caiTiei-" or '-lalrr'" a- u-cd above are ('m])loved in the 

 sense of iiidlcnt i r.- tlie relatively l„\ver nr higher level 

 along a line of dex-elopnient, at which a grouj) branched 

 off, and is based npoii the coniparative anatomical primi- 

 tiveness of tlie gi-onj) under consideration. In the case 

 of the Coleoptera, Handlirsch maintains that they are 

 paleontologically older than the Dermaptera, and if sub- 

 sequent findings should corroborate this view, it would 

 be necessary to search for the origin of the Coleopteron 

 line of development lower down on the Plecopteron stem 

 than the point at which the Dermaptera branched off to 

 follow their own path of specialization, but the Dermaptera 

 are <(> iniieh ini>r(^ lowly (n'u-anized than the ('oleoptera, 

 to which they jiri- aiiat(.iiiie;il!y very >iiiiihir (see also 

 Crami)ton, l!>lS/>), that I am inclim-d t<. believe that the 

 lack of earlier Dermajiteron remains is due to the incom- 



