HEMIMETABOLIC INSECTS. 



593 



dichotomise ; stout and well-defined cross-veins rare ; membrane 

 generally reticulate. "Wings in repose lying on the abdomen, the 

 anal area of the hind-wings, though usually of great distal extension, 

 never plaited, though sometimes broadly folded. Abdomen usually 

 long and slender, the last joint often furnished with simple articu- 

 lated appendages " (Scudder). 



The Palceodictyoptera, as above defined, comprise generalised 

 Insects, in which there was an " incomplete " metamorphosis, and 

 the four wings were membranous, equally developed, and charac- 

 terised by a simple type of neuration. Mr Scudder recognises 

 within the limits of the Palceodictyoptera four principal types of 

 structure, representing the existing orders of the Orthoptera, Neu- 

 rofitera, Hemiptera, and Coleoptera, and in accordance with this 

 he has divided the order into four primary groups (the Orthopteroid, 

 Neuropteroid, Hemipteroid, and Coleopteroid groups). The earliest 

 known form of the Palceodictyoptera is the Palceoblattina Douvillei 

 of the Silurian rocks of Calvados, which is at present the most 

 ancient representative of the entire class of the Insects, and the 

 affinities of which are uncertain. Other forms of the order appear 

 in the Upper Devonian rocks of 

 North America ; numerous Carbon- 

 iferous and a few Permian forms 

 are known ; and the last represen- 

 tatives of the order appear in the 

 Triassic rocks of North America. 



The Orthopteroid section of the 

 Palceodictyoptera includes a group of 

 forms representing the modern Cock- 

 roaches, and a second group which 

 shows relationships to the existing 

 " Stick-insects " [Phasmidce). Apart 

 from the Silurian genus Palceoblat- 

 tina^ various Carboniferous types 

 are known which are allied to the 

 existing Cockroaches, but differ 

 from these in the neuration of the 

 wings ; and upon such have been 

 founded the genera Archimylacris, 

 My/acris, Progonoblattina (fig. 443), 

 Etoblattina, &c. Of these, the last- 

 mentioned genus occurs also in the 

 Trias of North America, along with 



other allied forms. The precursors of the modern Phasmidce are 

 the " Protophasmids " of the Carboniferous rocks, comprising various 

 genera which resemble the existing " Stick-insects " in the form of 



vol. 1. 2 p 



Fig. 443. — Progonoblattina helvetica, art 

 Orthopteroid type of the Palceodictyoptera, 

 from the Carboniferous rocks of Switzer- 

 land, restored. (After Heer.) 



