INSECTS OF NEW BRUNSWICK. 33 



structurally defined areas is polygonal and tolerably regular, instead of being simply quad- 

 rate ; while the intercalated veins are all connected at their base, instead of being free. 

 Xenoneura also, as compared with modern Sialina, show.-i what should perhaps be deemed 

 a higher (or at least a later) type of structure, in the amalgamation of the externomedian 

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

 lateral attachments of the internomedian veins; in the minuter and feebler cross 

 venation, however, it has an opposite character. 



12. We appear, therefore, to he no nearer the beginning 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 advantage than the 

 carboniferous types in support of any special theory of the origin of insects. All such 

 theories have required some Zoaea, Leptus, Campodea, or other simple wingless form as 

 the foundation point; and this ancestral form, according to Haeckel at least, must be 

 looked for above the silurian I'ocks. 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 injects 

 with rather highly differentiated structure, which, taken together, can be considered 

 lower than the mass of the upper carboniferous insects, only by the absence of the very 

 few Hemiptera and Coleoptera 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 which, to some degree, bear out 

 expectations based on the general derivative hypothesis of structural development, 

 there are quite as many which are altogether unexpected, and cannot be explained by 

 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 

 sub-order to which they belong, itself one of the very lowest sub-orders. 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 con- 

 fidentially asserted that they are higher in structure than most of the carboniferous 

 types, and exhibit syntheses of character differing from theirs. It is quite as if we 

 were on two distinct lines of descent when we study the devonian and the carbon- 

 iferous insects ; they have little in common, and each its peculiar comprehensive types. 

 Judging from this point of view,' it would be impossible to say that the devonian 

 insects showed either a broader synthesis or a ruder type than the carboniferous. This 

 of course may be, and in all piobabiHty is, because our knowledge of carboniferous 

 insects is, in comparison, so much more extensive ; but, judging simply by the 

 facts at hand, it appears that the carboniferous insects cai-ry us back both to the 



