CHAPTER VII 



THE ORDER APTERA DEFINITION CHIEF CHARACTERISTICS 



THYSANURA CAMPODEA JAPYX MACHILIS LEPISMA 



DIVERSITY OF INTERNAL STRUCTURE IN THYSANURA ECTO- 



TROPHI AND ENTOTROPHI - - COLLEMBOLA LIPURIDAE - 



PODURIDAE SMYNTHURIDAE THE SPRING THE VENTRAL 



TUBE ABDOMINAL APPENDAGES PROSTEMMATIC ORGAN 



TRACHEAL SYSTEM ANURIDA MARITIMA COLLEMBOLA ON 



SNOW LIFE-HISTORIES OF COLLEMBOLA FOSSIL APTERA 



APTERYGOGENEA ANTIQUITY AND DISTRIBUTION OF CAMPODEA. 



Order I. Aptera. 



Small Insects with weak outer skin, destitute throughout life of 

 wings or their rudiments, hut with three })airs of legs ; an- 

 tennae large or moderate in size. 



THE above definition is the only one that can at present be 

 framed to apply to all the Insects included in our Aptera. 

 Unfortunately it is far from diagnostic, for it does not enable 

 us to distinguish the Aptera from the larvae or young indi- 

 viduals of many Insects of other Orders. There are, however, 

 certain characters existing in many species of Aptera that enable 

 their possessors to be recognised with ease, though, as they are 

 quite wanting in other members, they cannot correctly be in- 

 cluded in a definition applying to the whole of the Order. 



We are thus brought in view of two of the most important 

 generalisations connected with the Aptera, viz. that these Insects 

 in their external form remain throughout their life in a condition 

 resembling the larval state of other Insects, and that they never- 

 theless exhibit extreme variety in structural characters. 



The more important of the special characters alluded to above 



