THE STRUCTURE AND LIFE OF INSECTS 245 



they are united, and the pair of jointed tails which project 

 behind. The tails have probably some real use, but it 

 would be hard to explain what it is. Some have thought 

 that they serve as feelers in the dark recesses where the 

 cockroach lurks, and give warning of the approach of 

 dangers from behind. In a cricket they look very like 

 a hind pair of antennae. 



The breathing organs of an insect are more easily demon- 

 strated in a caterpillar than in a cockroach. It is easy 

 to prepare a piece of the integument of one side, which 

 will, with the help of the lantern, display the spiracles 

 with admirable clearness. The branched air- tubes may 

 be exhibited either in the form of a microscopic prepara- 

 tion or a photograph from the same. The alimentary 

 canal of a cockroach and a great part of its nerve-cord 

 can, if desired, be mounted as lantern-slides. 



The simple lens is an excellent aid to the study of insect 

 structures. A lens, magnifying five or six diameters and 

 suitably mounted, is not expensive, 1 but, where handicraft 

 is practised, it is better to buy nothing but the glass lens, 

 and make your own dissecting microscope in the school. 

 (See Scherren's "Through a Pocket Lens.") 



The study of enlarged preparations and of living insects 

 may be accompanied or followed by some such remarks 

 as follow. 



WHAT is AN INSECT ? 



An insect belongs to the large group of Arthropod 

 animals, which all have the body defended by a jointed 

 chitinous armour. Not only the body but the legs also 

 are jointed, hence the name " Arthropod," which means 

 " with jointed feet." Among the arthropods which are 

 not insects come the crayfish and other crustaceans, the 

 spiders and scorpions, the centipedes and millipedes. 

 An insect is sufficiently defined as a six-legged, air-breath- 

 ing arthropod. 



1 Leiiz of Wetzlai makes a good one for 8s. 



