THYSANURA. 83 



cavity of the head, and also on account of the small size of 

 the insects. Figure 89 represents them in place in the 

 head, and also each separately. 



In certain respects these insects represent a connecting- 

 link between the other six-footed insects (Hexapoda) and 

 the Myriapods ; for many of the Thysanura have rudiments 

 of legs on the abdomen. It is believed, therefore, that they 

 are much like the first insects that appeared on the earth 

 in ancient geological times. 



The Thysanura undergo no metamorphosis, the young 

 resembling the adult in form. 



The name of the order is from two Greek words: 

 thysanos, a tassel ; and oura, the tail. 



The Thysanura include two distinct types of insects ; 

 these are classed as suborders, and can be distinguished by 

 the following table : 



TABLE OF THE SUBORDERS OF THE THYSANURA. 



A. With bristle-like and many-jointed appendages at the caudal end 

 of the body (in a single genus these appendages are in the form of 

 forceps, Fig. 91), and without a sucker on the ventral side of the 

 abdomen, p. 83 ClNURA. 



AA. With a forked sucker on the ventral side of the first abdominal 

 segment. Abdomen with a springing apparatus near its caudal 

 end, or without appendages, p. 84 COLLEMBOLA. 



Suborder ClNURA (Ci-nu'ra). 

 The Bristle-tails. 



Often the careful housekeeper sees in the ironing-basket, 

 or upon the book-shelf where she is dusting, a flash of light 

 like a tiny thread of quicksilver, that usually vanishes as soon 

 as seen. 



If she is experienced she knows that this streak of light is 

 a little animal, half an inch long, whose body is clothed in 

 shining scales like those of a fish. Hence she calls it a Fish- 

 moth. Its scientific name is Lepisma saccharina ; (Le-pis'ma 

 sac-cha-ri'na) ; it is especially abundant in warm climates, 



