MYRIAPODA 333 



(2) the Diplopoda, or millipedes. The first undoubted 

 representatives of the Chilopoda occur in the amber found 

 in the Oligocene Beds of Prussia; the Diplopoda have also 

 been found mainly in this amber, but one form, which 

 perhaps belongs to this Order, was discovered in the 

 Cretaceous rocks of Greenland. 



The Palaeozoic Myriapods differ considerably from the 

 later representatives of the group and are regarded by 

 Scudder as constituting two distinct Orders which are 

 confined to the Palaeozoic formations. The earliest 

 examples are found in the Upper Silurian of Lanarkshire 

 and belong to the genus Ar chides mas. In the Old Red 

 Sandstone of Scotland Kampecaris and ArcJiidesmus occur. 

 A larger number of forms (Xylobius, Euphoberia, Pattonia, 

 Anthracodesmas) are found in the Carboniferous and 

 Permian rocks. 



CLASS IV. INSECTA 



The body of an insect can be separated into head, 

 thorax, and abdomen. The head is formed of fused 

 segments ; it bears four pairs of appendages — one pair 

 of antennae, one of mandibles, and two of maxillae. In 

 the thorax there are three segments, each bearing one 

 pair of legs ; the second and third segments usually carry 

 a pair of wings on their dorsal surfaces. The abdomen is 

 composed of several (commonly ten) segments, and is 

 usually without appendages. Insects breathe by means 

 of tracheae. 



No undoubted Insects are at present known from the 

 Devonian or earlier formations. But in the Coal Measures 

 and in the Permian the group is represented by a con- 

 siderable variety of forms. Remains of insects have been 



