Legs of Insects. 51 



1, 2, 3), while in the Melipona there are only two. The ribs 

 or veins consist of a tube within a tube, the inner one form- 



Ficj. 9. 



Thorax of Bee magnified three times. 

 a, u, a — Muscles. 6, 6— Crust. 



ing an air tube, the outer one carrying blood. On the costal 

 edge of the secondary wings we often find, hooks, to attach 

 them to the front wings (Fig. 3, B, a). 



The wings are moved by powerful muscles, compactly loca- 

 ted in the thorax (Fig. 9, a, a, a), the strength of which is 

 very great. The rapidity of the vibrations of the wiiigs 

 when flight is rapid, is really beyond computation. Think of 

 a tiny fly outstripping the fleetest horse in the chase, and then 

 marvel at this wondrous mechanism. 



The legs (Fig. 2, g, g, g~) are six in number in all mature in- 

 sects, two on the lower side of each ring of the thorax. These 

 are long or short, weak or strong, according to the habit of 

 the insect. Each leg consists of the following joints or parts: 

 The coxa, which moves like a ball and socket joint 

 in the close-fitting coxal cavities of the body-rings. Next 

 to this follow in order the broad trochanter, the large, broad 

 femur (Fig. 2, g, 1), the long, slim tibia (Fig. 2, g, 2), fre- 

 quently bearing strong spines at or near its end, called tibial 

 spurs, and followed by the from one to five-jointed tarsi (Fig., 

 2, g, 3, 3, 3, 3, 3). AU these parts move freely upon each 

 other, and will vary in form to agree with their use. At the 

 end of the last tarsal' joint are two hooked claws (Fig. 2, g, 4), 

 between which are the pulvilli, which are not air-pumps as 

 usually described, but rather glands, which secrete a sticky 

 substance which enables insects to stick to a smooth wall, even 

 though it be above.them. The legs, in fact the whole crust, 

 are more or less dense and hard, owing to the deposit within 

 the structure of a hard substance known as chitine. 



