254 ENTOMOLOGY FOR MEDICAL OFFICERS 



and some of these protect themselves and their eggs with a 

 web. Books can be protected from book-lice by painting 

 with a spirit solution of perchloride of mercury ; creasote will 

 protect entomological collections. 



Order Thysanura : Bristle-tails. 

 (Gr. Ova-avos = tassel, and ovpd = tail.) 



In the zoological scheme this order is placed, along with 

 the next order, Collembola, at the bottom of the Class Insecta. 

 The members of both orders are small, wingless insects, and 

 some of them seem to have rather close affinities with some 

 of the Myriapoda. 



The order is named from the two or more long antenna- 

 like filaments that project from the last abdominal segment. 



The Thysanura are fragile, wingless insects of no great 

 size, and they do not undergo a metamorphosis : the antennae 

 are long and are composed of a multitude of segments, and 

 the abdomen consists of lO visible segments. They are 

 common in damp and dark places, particularly in the tropics. 

 The Silver fish-insect, Lepisma, is a good example of the 

 order — an active little insect, covered with silvery scales, 

 which hides among books and papers: a common Calcutta 

 species of Lepisma certainly feeds on these things, and also 

 on cloth. 



Order Collembola : Springtails. 

 (Gr. KhWa. = glue, and lii^o\os = a peg.) 



The insects of this order are named from the coarse tube which pro- 

 jects from the ventral surface of the ist abdominal segment, and is 

 supposed to be adhesive. Their popular name of Springtails is derived 

 from the existence, in many of them, of a pair of long, stiff filaments, 

 placed near the end of the body and flexed under the abdomen — the 

 sudden extension of which produces a jump. 



The order includes minute, wingless insects which do not go through 

 any metamorphosis. The antennae have few (4 to 6) segments, and the 

 legs have no tarsus. Springtails are found in damp places on land, and 

 some are aquatic both in fresh water and in the sea. They are said to 

 be common on snow, and uncommon in dry and hot regions. 



We have now done with all those orders of insects that 

 include species which the medical officer is justified in regard- 



