THYSANOPTERA. 201 



not only furnishes the colouring matter called lac-dye, but causes also an exudation 

 of a resinous substance, gum-lac, from the bark of the trees on which it lives. 

 Stick-lac is the name given to this substance in its native state while still adhering 

 to the twigs of the tree ; when separated, pounded and freed by washing from its 

 colouring matter, it is known as seed-lac, which after further preparation becomes 

 lump-lac or shellac. 



The Pediculina, or true lice, as distinguished from the bird-lice of the order 

 Orthoptera, are provided with piercing and suctorial mouth-parts, and live on 

 the blood of animals, to which by this means they are enabled to gain access. 

 Though they are without wings, and were at one time associated with other 

 wingless insects in a separate order, lice are now generally regarded as de- 

 graded forms of Rhynchota, in which the 

 wingless condition has been brought about 

 as an adaptation to their parasitic life. In 

 these insects the head is set horizontally, and 

 carries short, cylindrical, and usually five- 

 jointed antennae; the eyes are small and ^head-louse with its eggs ; 2, body- louse ; 

 simple ; and the mouth consists externally of 3, crab-louse. (All greatly enlarged.) 



a soft, retractile beak, somewhat conical in 



shape, and furnished below with a row of hooks for attachment. Within the 

 fleshy beak there are four grooved pieces, forming by their juxtaposition an inner 

 membranous tube, which can be extended beyond its sheath, and acts both as a 

 piercing organ and as a conduit for the passage of the blood which is sucked up by 

 the insect. The thorax is small and not distinctly divided into segments, while the 

 abdomen is relatively large, generally somewhat elliptical in outline, and exhibits 

 seven or eight clearly marked segments. The tarsi are two -jointed, with the 

 second joint in the form of a claw which can be turned back towards the first. 

 Lice multiply rapidly, one generation succeeding another in a short space of time. 

 Their pear-shaped eggs are generally found attached to the bases of the hairs ; the 

 young, which are hatched after about eight days, undergo no metamorphosis, and, 

 in some cases, require only about eighteen days before becoming adult. 



Order Thysanoptera. 



The insects comprised in this order — some of them familiar enough to gardeners 

 and others, by whom they are known as thrips — are all small. A few species only 

 exceed four or five lines in length, while the great majority are less than a tenth 

 of an inch long. They are distinguished from all other insects by certain 

 peculiarities in the structure of their mouth and of their wings and tarsi. The 

 mouth lies far back on the under side of the head ; its mandibles are transformed 

 into a pair of piercing setae, while the upper lip, maxillae and labium — the two 

 latter, provided with short palpi — are united together to form a short suctorial 

 tube. The wings are small and narrow, contain few nervures, and are thickly 

 fringed all round with long hairs. Two pairs of such wings are generally present, 

 but in some cases they may be rudimentary or altogether wanting. The tarsi, 

 which consist of one, two, or three joints, are without claws at the end, but are 



