APTERA 



ISI 



as being possessed by some but not by all members of tlie Order 

 are (1) a remarkable leaping apparatus, consisting of two 

 elongate processes 



at the under side of the termination of the 

 body; (;]) a peculiar ventral tube, usually seen in the condition 

 of a papilla with invaginated summit, and placed on the first 

 abdominal segment (see Fig. 100, p. 194); (3) the scales cover- 

 ing the body ; (-4) the existence of abdominal appendages in the 

 form of long cerci or processes at the termination of the body, or 

 of short processes on the sides of the under surface of the abdominal 

 segments. 



Throughout the Order the general shape approximates to 



that of a larva ; this is 

 the body of Machilis 

 (Fig. 90). There is a 

 succession of rings 

 differing little from 

 one another, except 

 so far as the head is Fio. 90. 

 concerned ; even the 

 division of thorax from 



shown by the 



diagrammatic section of 



-Section of body of Machilis : 

 (After Oudemans. ) 



0, ovipositor. 



abdomen is but little evident, and 

 although in some of the forms the three thoracic segments may 

 differ considerably among thenrselves, yet they never assume the 

 consolidated form that they do to a greater or less extent in the 

 imago stage of the other Orders. Fig. 90 > shows the larva-like 

 structure of the body, and also exhibits the inequalities in size 

 between some of the dorsal and the corresponding ventral plates. 

 This phenomenon is here displayed only to a small extent, so 

 that the true relations of the dorsal and ventral plates can be 

 readily detected ; but in the higher Insects want of correspond- 

 ence of this kind may be much more extensive. 



The respiratoi-y system is in many of these Insects very 

 inferior in development, and may even be, so far as tracheae and 

 spiracles are concerned, entirely absent, but in other members of 

 the Aptera it is well developed. In the other internal organs 

 there is also great variety, as there is in the external structure. 



A brief explanation as to the term Aptera, which we have 

 adopted as the name of this Order, is necessary. This name was 

 used by Linnaeus for our Insects, but as he associated with them 

 various other heterogeneous forms which were afterwards 

 separated, his " Aptera " became completely broken up and ceased 



