384 CHARACTERS OF INVERTEBRATE ANIMALS 



Order 9.— WINGLESS INSECTS (Aptera) 



This is a group of small inconspicuous insects which are of 

 great interest theoretically, as they are probably to be regarded 

 as insects in their simplest form, i.e. are of " primitive " nature. 

 They never possess any traces of wings, nor do they appear to 

 be descendants of winged ancestors, as is the case with the 

 numerous wingless insects placed in other groups. The segmen- 

 tation of the body is more clearly marked than in other insect 

 orders, and the segments are not so specialized, besides which small 

 abdominal appendages are not uncommon. The horny covering 

 of the body is comparatively delicate. Two sub-orders are 

 recognized: — i. Tassel -Tails [Thysanura) and 2. Springers 

 {Collembola). 



1. Thysanura. — The most marked feature of the sub-order 

 consists in the presence of two or three long styles projecting 



from the hind end of the body. Pro- 

 bably the commonest British species is 

 the Silver- Fish {Lepis-ma saccharind) 

 (fig. 233), found in brown sugar and old 

 books. It possesses three tail-filaments, 

 and its silvery lustre is due to the pre- 

 sence of peculiar scales, which make 

 Fig. 233. -Aptera (magnified) beautiful microscopic objects. Another 



I oS'tiit^^Xr^^S^!' species, common in the crevices of rocks 



at the sea-side, is Machilis maritima, 



which is not unlike the preceding, but grey in colour instead of 



silvery. 



2. Collembola. — Many, but by no means all, of these possess a 

 curious springing apparatus in the form of two stiff bristles which 

 can be folded under the body and secured by a sort of catch 

 projecting from the third segment. When released the animal 

 is thrown into the air much like the "jack-jumper" children 

 are so fond of fabricating from the "merrythought" of a goose. 

 They are common under bark, dead leaves, stones, &c., and 

 one species {Podura aquaticd) may often be seen floating 

 on the surface of stagnant pools. Some kinds are abundant 

 in Alpine regions, on the surface of snow or ice, and among 

 these may be mentioned the Glacier-" Flea" {Desoria glacialis) 

 (fig. 233). The Collembola are not all provided with a springing- 



