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- 



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



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

 leinbola and Thysanura, the Mallophaga, and the Pedicu- 

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

 no metamorphosis. 



The Collembola and TJiysanura undergo no metamorpho- 

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

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

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

 mandibles and maxillae, 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 Anoma the mouth is 

 suctorial. 



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

 * Ibid., V .S7. 



