EXTERNAL ANATOMY 35 



Abdomen. — The third, largest, and most important region of 

 the body is the abdomen. It is of importance because it contains 

 the organs of reproduction and their external opening and the 

 greater part of the structures that excrete the wax for covering the 

 body and the eggs. The abdomen consists typically of ten seg- 

 ments. In the Diaspidinae the segments of the caudal half are 

 fused and the coriae are wanting. Systematists have made no use 

 of the number of abdominal segments and usually those who have 

 described and figured the abdomen have not always been consistent 

 in giving the same number for the same species. The dorsal aspect 

 of each segment is known as a tergum and the ventral aspect as a 

 sternum. 



The abdomen in the Diaspidinae is divided into two regions. 

 The cephalic portion consists of four segments with distinct flexible 

 coriae, the preabdomen, and a strongly chitinized caudal portion 

 without coreae, the pygidium. The adult females of the Conchas- 

 pinae are described as having a pygidium, but the coriae can be 

 identified between practically all of the segments and they are 

 provided with cerores instead of ceratubae as in the Diaspidinae. 

 In the abdomen of the adult Lecaniinae all the segments are fused 

 and the coriae obsolete, but the coriae can frequently be identified 

 in the nymphal stages, particularly the first. 



The segmentation of the body can be determined or approxi- 

 mated in many species of coccids even if the legs are wanting 

 and the intersegmental coriae are obsolete. This can be accomp- 

 lished by means of the row of setae, cerores, or setae and cerores 

 placed along each lateral margin or around the periphery of the 

 body. The setae of these rows are generally larger or different 

 in form from the other setae of the body so that they can be 

 readily recognized and their intersegmental homology determined. 

 In the first stage nymphs of Icerya these structures are large setae 

 placed on prominent chalazae while in Pseudococcus they are 

 groups of short conical setae, usually one to six, surrounded by the 

 tricerores which form the prominent pencils of wax projecting 

 from the periphery of the body in all the nymphal stages and the 

 adult. While there is some variation among the different species 

 and genera as to the number and nature of these groups, they are 

 always constant for a given species. The usual arrangement is a 

 single group on each side of each abdominal segment, two to three 

 groups on each side of each thoracic segment, and four to six 

 groups on each half of the head. The components of the cephalic 



