260 Mr. S. H. Scudder on Devonian Insects. 



veins for a long distance from the base, and in the peculiar 

 structure and lateral attachments of the interno-median veins ; 

 in the minuter and feebler cross venation, however, it has an 

 opposite character. 



12. We appear^ therefore^ to he no nearer the heginning of 

 things in the Devonian epoch than in the Carboniferous, so far 

 as either greater unity or simplicity of structure is concerned ; 

 and these earlier forms cannot be used to any better advan- 

 tage than the Carboniferous types in support of any special 

 theory of the origin of insects. All such theories have re- 

 quired some Zoea, Leptus, Campodea, or other simple wing- 

 less form as the foundation-point ; and this ancestral form, 

 according to Hackel at least, must be looked for above the 

 Silurian rocks. Yet we have in the Devonian no traces 

 whatever of such forms, but, on the contrary, as far down as 

 the middle of this period, winged insects with rather highly 

 differentiated structure, which, taken together, can be consi- 

 dered lower than the mass of the Upper Carboniferous insects 

 only by the absence of the very few Hemiptera and Coleo- 

 ptera which the latter can boast. Remove those few insects 

 from consideration (or simply leave out of mind their future 

 ■development to very distinct types), and the Middle Devonian 

 insects would not suffer in the comparison with those of the 

 Upper Carboniferous, either in complication or in diversity of 

 structure. Furthermore, they show no sort of approach 

 toward either of the lower wingless forms hypothetically 

 looked upon as the ancestors of tracheate Articulata. 



13. Finally, while there are some forms tvhich to some degree 

 hear out expectations hased on the general derivative hypothesis 

 of structural development, there are quite as many which are 

 altogether unexpected, and cannot he explained hy that theory 

 without involving suppositions for which no facts can at present 

 he adduced. Palephemera and Gerephemera are unquestionably 

 insects of a very low organization related to the existing may- 

 flies, which are well known to be of inferior structure as com- 

 pared with other living insects ; these may-flies are indeed 

 among the most degraded of the suborder to which they 

 belong, itself one of the very lowest suborders. Dyscritus too 

 may be of similar degradation, although its resemblance to 

 Homothetus leaves it altogether uncertain. But no one of 

 these exhibits any inferiority of structure when compared 

 with its nearest allies in the later Carboniferous rocks ; and 

 they are all higher than some which might be named ; while 

 of the remaining species it can be confidently asserted that 

 they are higher in structure than most of the Carboniferous 

 types, and exhibit syntheses of character differing from theirs. 



