284 GLOSSARY 



the material, in the form of a viscous fluid, is forced in two very 

 delicate streams, which unite, and on exposure to the air harden 

 into a single continuous thread of silk. 



Spiracles. The breathing-pores or apertures whereby the internal 

 respiratory system, or breathing tubes (tracheae) of insects, com- 

 municate with the air. Usually 'situated along the sides of the 

 body, and do not occur on the head. Their number varies, but 

 there is never more than one pair on a single segment of the body. 

 A common form of structure consists of a horny oval ring, within 

 which is a valve, made up of converging fibres, guarding the ex- 

 ternal entrance. At a short distance within this valve a second may 

 be found, of more complicated form. 



Spiral. Winding like a screw. 

 Succulent. Juicy, moist. 



Sucker-feet. See Prolegs. 



Suctorial. Adapted for sucking. 



Tarsus. (pi. tarsi) The fourth chief division of the leg in insects, 

 that which is popularly called the foot. It is made up of segments, 

 but is liable to numerous modifications. The distal segment bears 

 one or more claws, which are sometimes strongly toothed, so that 

 there may appear to be four, or even six, claws. 



7^awny, A pale yellow. 



Tegument.^Cover, skin. 



'Thoracic. Of, or relating to, the thorax. 



Thorax. The second or intermediate region of the body. Formed of 

 three segments, known respectively as the'pro-thorax, meso-thorax 

 and meta-thorax. Readily recognised for its appendages, viz. , 

 three pairs of legs, and never more than two pairs of wings. Each 

 segment bears one pair of legs, and in winged insects, the wings 

 are carried by the two hinder segments. 



Tibia. The third chief part or shank of the leg in the perfect insect, 

 coming between the thigh (femur) and the foot (tarsus). In insects 

 that burrow in the ground, this portion is much broadened, and 

 shaped somewhat like a hand. 



Tissue. The elementary or essential structures of which organs are 

 composed. 



Trachea. Breathing-tubes of insects communicating with the outside 

 by small mouths, or pores (spiracles). By means of branching, 

 these tubes carry the air through every portion of the insect, so 

 that the various tissues are supplied with oxygen without the inter- 

 vention of blood, as in the higher animals. The walls of these air- 

 tubes, like the body-wall, are made up of three layers, and the 

 outer layer of the wall of the body corresponds with the inner 

 layer of the wall of the tube. The latter is shed, with the outer 

 skin of the body, when the larva moults. In many adults with 

 powerful flight, the tracheae are dilated into numbers of minute sacs. 



Trimorphic. A species is so designated which presents three distinct 

 forms. 



Tubercle. A small protuberance. 



Ttiberculated. Possessed of tubercle-like prominences. 



