THYSANURA. 



67 



seen to be of different shapes, being marked by parallel 

 longitudinal lines, and are fastened to the body by a 

 short stem. The body is somewhat 

 flattened, and the thoracic rings {b' , 

 b'\ b'") overlap each other slightly. 

 The head possesses a pair of very 

 small eyes {n'), which are widely 

 separated, and the antennae (af) are 

 long and well developed. The mouth ^,, 

 parts are of the biting type, and the 

 insects often do much damage to 

 furniture when houses are closed for 

 the summer. Within a year we have 

 seen cotton window-shades badly 

 eaten by these creatures. The three 

 pairs of legs are used in running, and 

 the silvery scaled insect glides so 

 swiftly along it is known as the " sil- 

 ver fish," " silver witch," and " fish- 

 moth." The anterior abdominal 

 appendages found in Campodea are 

 sented in Lepisma by clusters of stiff hairs, but 

 the abdomen carries at its extremity three long bris- 

 tles, and also one pair of short, curved bristles. 



The respiratory system in Lepisma is simple as 

 compared -with that of the locust and other flying 

 insects. The tracheae are present, but not the air- 

 sacs. The absence of these, like that of the wings, 

 is also characteristic of the larvae of other insects, 

 although their adults may possess them. 



Teachers will find it instructive to observe Lepisma 

 as a full-grown insect, and then compare it with the 



Fig. 28. 



only repre- 



