266 MYBIAPODA INSECTA. 



proves that the Arachnida were represented in the fauna ot 

 the primary epoch, and supplies another link to the chain of 

 evidence afforded by the flora of that stage, that the tempera- 

 ture of the centre of Europe resembled that of our tropics at 

 the .time when the coal plants flourished. Fossil spiders are 

 found in the yellow amber of Prussia. Koch and Berendt 

 have described one hundred and twenty-three species be- 

 longing to fifty genera, of which thirteen are extinct, whilst 

 none of the species are identical with those now living. 



CLASS V. MTEIAPODA) 



The Centipedes have the body composed of twenty-four 

 feet or upwards". "All the members of this class are terres- 

 trial, and breathe by trachea. They live concealed under 

 stones, moss, or the bark of trees. Extinct genera of 

 IULIDJB and SCOLOPEKDRID^] have been found with those of 

 the preceding class by the same observers. 



CLASS VI. INSECTA. 



The Insects have the body divided into head, thorax, and 

 abdomen. The head is formed by the fusion of several 

 elements, and supports the eyes, the antenna?, and the parts 

 of the mouth. The thorax is composed of three segments 

 soldered together ; the pro-thorax, or anterior ; mesa-thorax, 

 or middle; and meta-thorax, or posterior. Each segment 

 supports one pair of articulated feet; and the pro-thorax 

 and meso-thorax the first and second pairs of wings, when 

 they exist. 



The abdomen consists of a series of simple rings, moveable 

 on each other, and without appendages, except the last pair, 

 which are sometimes provided with special organs. The 

 tegumentary skeleton is indurated with chitine, which has a 

 firmness equal to that of horn. Insects breathe by stigmata 

 or air-holes situated on the sides of the rings, and by trachea 

 or air- tubes, that ramify through all parts of their bodies. We 

 find representatives of most of the orders in a fossil state. 



Order DIPTERA (or Plies). Have two membranous 

 wings, articulated to the pro-thorax, and rudimentary wings 

 or balancers to the meta-thorax. 



