60 CLASSIFICATION OF INSECTS. 



of winged insects which sprang from the sides of the 

 wingless, primitive or Thysanuran stock. 



The difficulty of representing satisfactorily by any 

 linear arrangement the relations of the orders to each 

 other and to Thysanura has compelled us to give dia- 

 grams I -III. Diagram I., p. 60, shows by parallel bars 

 rising above the circular plate, which represents the 

 surface of the earth, the sixteen orders of insects as 

 they exist to-day, and below this plate the different 

 orders are arranged in converging bars according to 

 their supposed relations during geologic times. This 

 last is purely theoretical, since the present state of 

 our knowledge of fossil insects is too fragmentary and 

 unsatisfactory to afford sufficient evidences for the 

 demonstration of such a classification. 



Diagram II., p. 60, represents the opposite or farther 

 side of Diagram I., the plate having been turned around 

 so that the orders X.-XVI. can be more clearly seen 

 both above and below the earth's surface. Diagram 

 III., p. 61, is a view from above the circular plate 

 giving in horizontal section the position of the orders. 

 Diagrams I., II., A represents the wingless, primitive, 

 , or Thysanuran stock. The stems B, B'\ B'''} Dia- 

 gram I. ; B\ B^^, Diagram II., represent the winged 

 stocks which sprang from A. These may have been 

 composed, so far as the facts now known are con- 

 cerned, of a number of separate or branching lines 



1 B"^ extends in the diagram to the orders Hemiptera and 

 Thysanoptera instead of to the stem from which these orders 

 sprang. It is placed here because the stem proper is out of 

 sight, being farther down and behind B and ^". 



