CATALOGUE OF INSECTS. 7 



CHAPTER II. 



DEVELOPMENT OF INSECTS. 



Insect life was among the earliest that appeared on the earth. Just 

 when it did appear, or what it was like at first, we cannot say- 

 definitely, because soft-bodied creatures without bones or chitinous 

 external skeleton are not readily preserved in the rock, or, when 

 present, are easily overlooked if not absolutely irrecognizable. We 

 are therefore driven to more or less theoretical conclusions, based 

 upon what has been found in the rocks and upon what still exists 

 with us. 



We find reason to believe then that the primitive insect from which 

 the vast variety now existing has been developed was a small, soft- 

 bodied creature, living in mud or in moist earth along the banks of 

 bodies of water. It had six legs, no wings, probably abdominal 

 appendages other than legs, no compound eyes or no eyes at all, and 

 no developed breathing system ; taking in oxygen from the sur- 

 rounding moisture through all parts of the skin surface. The head 

 was not much differentiated from the rest of the body and the mouth 

 parts were generalized, i. e., neither typically fitted for biting nor for 

 piercing, though three or four pairs of fleshy processes contained the 

 possibilities of both types. Creatures very much like that just 

 described exist at the present time and form part of the order Thysa- 

 nura. In some of the forms of that order now existing mandibles 

 occur, and in others they are, if present at all, in the form of straight 

 processes, unfitted for chewing. These insects have no metamor- 

 phosis and usually live in damp places, feeding on decaying substances. 



Our primitive Thysanurans developed first of all into two branches 

 according to mouth structure — some becoming fitted for chewing 

 their food, while others became fitted to puncture and suck. In 

 both of these branches wings developed, quite different in type, yet 

 with a similar scheme in venation ; Cicada, according to Comstock, 

 representing a most generalized condition. 



The little order Thysanoptera has the mouth fitted for puncturing 

 or scraping the leaf surface, getting at the plant juices in that way, 

 while the wings are long, narrow, frail and with long fringes, from 

 which the ordinal name is derived. They are unfavorably known to 

 the farmers as Thrips, and they often do serious injury to field crops 

 like onions and cabbage, and to nursery peach trees. 



A step forward is made in the Rhyngoia, in which the mouth parts 

 are developed into slender lancets fitted for piercing and protected by 



