CHAPTER I 



INTRODUCTORY 



FLEAS form a group of insects that have, until 

 recently, been little studied by zoologists. We call 

 them insects because they are jointed animals, or 

 Arthropods, with three pairs of legs in the adult 

 condition. The reader will best understand the posi- 

 tion which fleas occupy in the general classification 

 of animals by remembering that the arthropods, or 

 jointed animals, are one of a dozen subkingdoms, 

 or phyla, to which the various members of the great 

 animal kingdom have been assigned. There is good 

 ground for believing that all the animals included in 

 each phylum trace their ancestry back to a common 

 primitive form which lived in more or less remote 

 ages. Besides (1) Insects, the arthropods, or jointed 

 animals, include (2) Crustaceans, such as crabs, 

 lobsters, shrimps, wood-lice, water-fleas and bar- 

 nacles ; (3) Myriapods, such as centipedes and 

 millipedes ; and (4) Arachnids, such as spiders, scor- 

 pions, mites and ticks. To all these varied forms of 

 animal life fleas, and other insects, are therefore more 

 or less nearly related. 



R. F. 1 



