34 THE COCCIDAE 



to identify even in stained mounted specimens. The mesofurcae 

 and metafureae are present in Icerya. The furcellae another 

 series of invaginated lobes forming a part of the endoskeleton of 

 the ventral aspect have not been identified. Each of the lobes of 

 the endoskeleton, apodemae or furcae, which are primitive struc- 

 tures, is often designated as an apodeme ; while other lobes which 

 are identical in form and structure but are secondary in origin 

 are known as parademes. 



Legs. — The legs are of the ordinary type and sequence of parts 

 of other insects. They appear much larger and longer in the 

 nymph of most species than in the adult because of the size of the 

 body. The profemur is greatly enlarged and dilated in the Mar- 

 garodinae and the protibia is fitted with a hook-like tarsus for 

 digging. 



The proximal segment of each leg, a coxa, is subglobular and 

 its proximal end is usually provided with a thickened rim. The 

 middle of the lateral margin of this rim or ring is provided with 

 an articular surface, an artis or coxartis, which articulates with a 

 coxacoila. The second segment or trochanter is oval or triangular 

 in outline. The largest sclerite or segment of the leg is the third 

 segment or femur. It is usually more or less compressed. The 

 suture between the femur and the trochanter is obsolete in certain 

 species of Orthezia. The fourth segment, the tibia, is usually longer 

 than the femur but smaller in diameter. The fifth segment is the 

 tarsus. Its distal end frequently bears long slender clavate setae, 

 which are known as tenant hairs, digitules, or empodial hairs. 

 They are probably the outlets of glands secreting a sticky substance 

 which aids them in clinging to smooth surfaces. The digitules 

 are more frequently present in the males than in the females. 

 The suture between the tibia and tarsus is always wanting in 

 species of Conchaspis and in certain species of Orthezia. The 

 tarsus consists of a single segment except the protarsus of the 

 males of Coccus and all the tarsi of the females of Exaeretopus, 

 which have two. The hook borne by each tarsus, a claw, is usually 

 not prominent and in some sj^ecies bears digitules. The digitules 

 of the legs are distinguished as the tibial digitules and the ungual 

 digitules. 



The comparative length of the various segments of the leg 

 is frequently indicated by systematists and used in the separa- 

 tion of species. This is usually stated in microns in a formula, as 

 follows: c. 120-140; tr. C^S: fem. 180-240; tib. 120-152; tar. 80-83: 

 claw 12-12. 



