222 THE COCCIDAE 



number of abdominal segments present in insects in general is 

 eleven. This number is readily recognized in many generalized 

 species of insects, but a study of the abdomen of several coccids 

 leads to the conclusion that the typical number of abdominal seg- 

 ments for this group is nine. That there has been a suppression 

 of the number of abdominal segments in other groups of insects is 

 easily proven. This suppression of segments may take place at 

 the caudal end, due to the modifications necessary to accommodate 

 the organs for copulation and for depositing the eggs, and at the 

 cephalic end, due apparently to the enlargement of the thorax to 

 accommodate the muscles for the organs of flight and its consequent 

 encroachment upon the cephalic abdominal segments. The ex- 

 planation of just how this reduction has taken place should be 

 sought, not only among the early nymphal stages of the female 

 coccids but especially among the groups showing less departure 

 from the progenitors of the coccids, the plant-lice and the psyllids. 



The abdomen in all diaspidids is divided into two regions, a ce- 

 phalic segmented region, the preabdomen, and a caudal unsegment- 

 ed region, the pygidium. The segmentation of the preabdomen is 

 always more distinct on the dorsal than on the ventral aspect. 

 The limits of the segments are generally indicated on each lateral 

 aspect by distinct constrictions. The preabdomen frequently 

 consists of four segments in the adult female, but in the first and 

 second nymphal stages and the adult females of certain genera, 

 one and sometimes more segments form a part of the preabdomen, 

 so that it may consist of five or six segments. 



The caudal, strongly chitinized, unsegmented pygidium in 

 the adult female consists typically of four segments. The pygidium 

 is strongly depressed so that the dorsal and ventral aspects are 

 close together. The lateral margins of the pygidium are provided 

 with projections and indentations which are known collectively as 

 the pygidial fringe. It is also designated simply as the fringe but 

 this term has already been used for the marginal band of glassy 

 threads of wax excreted from the octacerores in the Asterolecaniinae 

 and should be reserved for this use. The structure generally 

 designated as the pygidium is also known as the last segment or 

 anal plate. The early students of the Coccidae believed this 

 strongly chitinized caudal end of the abdomen represented a singl' 

 segment and hence the name of pygidium, but it is in fact a com- 

 plex of four or five segments. The number of segments and their 

 limits can only be approximated because all the coriae or sutures 



