DEVONIAN FAUNA. 147 



group of the netted -veins (Pseudoneiiroptera and Neuroptera), 

 although by some authors they, as well as all other Paleozoic 

 insects, are considered to represent a distinct, and now wholly 

 extinct, type of Insecta, the Palaeod.ictyoptera. In whichever way 

 their relationship be viewed, there can be little doubt that they 

 represent very nearly the lowest structural type of their class. It 

 is a very remarkable fact that the wing venation of these primi- 

 tive insect forms is practically identical with that which charac- 

 terises the modern insects belonging to the same group or order; 

 the vast lapse of ages between the Devonian period and our own 

 day appears to have efiected no essential modification of structure 

 in this particular direction. Besides these neuropterous forms, 

 certain wing fragments have been referred to the members of the 

 higher order Orthoptera, to which the modern grasshopper and 

 cockroach belong. But there seems to be considerable doubt as to 

 the claims of the so-called Devonian cockroach,* and it would, 

 perhaps, be as well to consider its position as still a matter of un- 

 certainty. The marked differentiation exhibited by the Devonian 

 insects indicates that they were far more numerous than would 

 appear from the paucity of their remains, and the inference drawn 

 as to their great antiquity has been confirmed by the discovery of 

 the Upper Silurian -form already referred to. Coincidently with 

 the appearance of these early inhabitants of the land surface, we 

 remark the first considerable development of a land vegetation, 

 whose earliest traces are to be met with in the Silurian period. 

 With but very few exceptions (certain forms, as Prototaxites, 

 Ormoxylon and Dadoxylon, considered by some authorities to 

 represent true conifers, the first of their kind) all the Devonian 

 plants belong to the lower or non-flowering division, the Crypto- 

 gamia, comprising a multitude of ferns, tree-ferns, giant representa- 

 tives, like Sigillaria and Lepidodendron, of the modern club-mosses 

 (Lycopodiacese), and scarcely less gigantic forms (Calamites, Cal- 

 amodendron, with Annularia, Asterophyllites, Sphenophyllum) be- 

 longing to the group of the horse-tails (Equisetacese). 



Of Invertebrata other than insects the Devonian fauna is very 

 rich in forms ; but these show a marked similarity to those of the 



* Eeferred by Hagen to the Neuroptera. The same authority considers 

 the age of the rock formation iu which the other insect remains have heeu 

 found as more likely Carhoniferous than Devonian. 



