28 INSECTS AND MAN 



at the base, as in the bugs, quite transparent, as in the plant 

 lice, or absent, as in the scale insects. Their mouths are 

 adapted for piercing and sucking. 



This is a varied order, its members assuming every im- 

 aginable shape and form, from the large- winged cicadas to 

 minute forms, having the appearance of flakes of bran. To 

 the uninitiated they resemble beetles, butterflies, and even 

 stick insects, according to their species. Mostly vegetable 

 feeders, some, however, the Reduviidce, are carnivorous, 

 certain species going so far as to attack man, whilst one 

 at least is known to transmit disease. The Membracidce 

 are remarkable for possessing horn-like projections of 

 the thorax; the Psyllidce are called manna insects: they 

 resemble miniature cicadas. The Pentatomidce, Coreidce, 

 Lygceidce are as varied in habit as they are in form. The 

 Coccidce or scale insects are, collectively, the most important 

 family in the insect world, from an economic point of view, 

 and, incidentally, the most harmful. As their popular name 

 implies, they cover themselves with a scale which acts as a 

 necessary protection from their enemies. 



This brief survey of the insect world makes no preten- 

 sions to completeness, but is given as a guide to the better 

 understanding of the ensuing pages. 



The orders are comprised of sub-orders and families, and 

 these again are made up of genera, each genus containing 

 one or more species. Taking the human flea, known in 

 scientific parlance as Pulex irritans, as an example, and 

 studying its relationship to other animals, we find that it 

 belongs to the division of Invertebrates, because it is pro- 

 vided with an exoskeleton, as opposed to an internal or en- 

 doskeleton ; it is an Arthropod on account of its segmented 

 body, to which are attached jointed appendages; seeing 

 that it has a distinct head, thorax, and abdomen, six legs 

 and antennae, it is a true insect ; being wingless and pro- 

 vided with a characteristic arrangement of its mouth parts, 

 together with other anatomical details, which do not con- 



