362 THE ANATOMY OF INVERTEBRATED ANIMALS. 



gnathites are changed in form and function, or become con- 

 fluent. 



The insects which, in this view of their morphological re- 



Fig. 102.— Campodea staphylinus, one of the Thysanura (after Lubbock). 1 



lations, occupy the lowest position in the group, are the Col- 

 lembola and Thysanura, the Mallopliaga, and the Pedicu- 

 lina, inasmuch as they possess no trace of wings and undergo 

 no metamorphosis. 



The Collembola and Thysanura undergo no metamorpho- 

 sis, and are always wingless. The abdomen contains six seg- 

 ments only in the Collembola (Podura, Smynthurus, Tomo- 

 ceros), in which group the mouth is usually provided with 

 mandibles and maxillse, though these, instead of being artic- 

 ulated with the sides of the head, are capable of being re- 

 tracted into its interior. 2 In the genus A?ioma the mouth is 

 suctorial. 



1 "Monograph on the Collembola and Thysanura" pi. liii. 



2 Ibid., p. 37. 



