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- 



Pxo. 102.— Campodea staphylinus, one of the Thysanura (after Lubbock).* 



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

 lemhola and Thysanura, the Mallophaga^ and the Pedicu- 

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

 no metamorphosis. 



The Collemhola and Thysanura undergo no metamorpho- 

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

 ments only in the Collemhola [Podura, S^nynthurus, 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.** In the genus Aiioma the mouth is 

 suctorial. 



» "Monograph on the Collemhola and Thysanura,'^'' pi. liii. 

 ^Ibid.^ p.' 37. 



