448 



AN INTRODUCTION TO ENTOMOLOGY 



The presence or absence of club-shaped thickenings of the dorsal 

 wall (paraphyses) that extend forward from near the bases of the 

 lobes (Fig. 523. :P)- 



The presence or absence of a thickening of the lateral margin of 

 the pygidium cephalad of the region in which the lobes are situated, 

 and resembling the lobes in structure (Fig. 523, m). 



The nimiber and shape of the thin projections of the margin, 

 known as plates. Two quite distinct types of plates can be dis- 

 tinguished: in one they are broad and fringed (Fig. 521, pe); the 

 plates of this type have been termed pectince; in the other type they 

 are spine-like in form (Fig. $21, pi); some writers restrict the term 

 plate to this type, and use pectince for the first type. Each plate 

 contains the outlet of a wax-gland. 



Fig. 523. — Part of the pygidium of Chrysomphalus tenebricosus , ventral aspect, 

 with the paraphyses {pp) of the dorsal wall showing through: /, /, /, lobes; 

 m, thickened margin; s, spine-like setee. 



The metamorphosis of coccids. — In this family the two sexes are 

 indistinguishable during the first nymphal stadium. Both are fur- 

 nished with legs, antenna, and functional mouth-parts. It is during 

 this period that the sedentary species spread over the plants that they 

 infest. In their subsequent development the sexes differ greatly; 

 hence the metamorphosis of each can be best discussed separately. 



The females never become winged. Some, as the mealy-bugs and 

 Orthezia, continue active throughout their entire or almost entire life; 

 but most forms become sedentary early in life and remain fixed upon 

 their host. Many species lose their legs and antennas when they 

 assume the quiescent form ; and in some the mandibular and maxillary 

 setse are wanting in the adult. The number of n>TTiphal instars in 

 females varies from two to four; the smaller number occurs in the 

 more specialized subfamilies. 



In the males there are usually four njonphal instars. During the 

 latter part of the nymphal life the male is quiescent, having formed a 

 cocoon or a scale within or beneath which it remiains till it emerges 

 as an adult. The stage of development at which the quiescent 



