26 AN INTRODUCTION TO ENTOMOLOGY 



In the present state of our knowledge of the affinities of the classes 

 of arthropods, it seems best to regard the Protura as representing a 

 separate class, of rank equal to that of the Pauropoda, Symphyla, etc. ; 

 and for this class I have adopted the name proposed for the group by 

 Berlese, that is the Myrientomata. 



The class Myrientomata includes a single order. 



ORDER PROTURA 



As this is the only order of the class Myrientomata now known it 

 must be distinguished by the characteristics of the class given above. 



Two families have been established : the Acerentomidae, charac- 

 terized by the absence of spiracles and tracheae ; and the Eosentomidae 

 the members of which possess two pairs of thoracic spiracles and 

 simple tracheae. 



That the Protura are widely distributed is evident from the fact 

 that in addition to those found in Italy representatives of the order 

 have been found in peat in Hampshire, England, and others have been 

 taken near New York City. 



CLASS HEXAPODA 

 The Insects 



The members of this class are air-breathing arthropods, with distinct 

 head, thorax, and abdomen. They have one pair of antennas, three pairs 

 of legs, and usually one or two pairs of wings in the adult state. The 

 opening of the reproductive organs is near the caudal end of the body. 



We have now reached in our hasty review of the classes of arthro- 

 pods the class of animals to which this book is chiefly devoted, the 

 Hexapoda,* or Insects, the study of which is termed entomology. 



Insects are essentiaily terrestrial ; and in the struggle for existence 

 they are the most successful of all terrestrial animals, outnumbering 

 both in species and individuals all others together. On the land they 

 abound under the greatest variety of conditions, special forms having 

 been evolved fitted to live in each of the various situations where 

 other animals and plants can live; but insects are not restricted to 

 dry land, for many aquatic forms have been developed. 



The aquatic insects are almost entirely restricted to small bodies 

 of fresh water, as streams and ponds, where they exist in great num- 

 bers. Larger bodies of fresh water and the seas are nearly destitute 

 of them except at the shores. 



*Hexapoda: hex (?), six; pous (irotfs), afoot. 



