EXTERNAL ANATOMY 33 



Thorax. — The thorax is divisible into three clearly marked 

 regions in most insects, the prothorax, the mesothorax, and the 

 metathorax. Such a condition does not exist among coccids. The 

 prothorax is usually continuous with the head, except in some 

 nymphs of the first stage, and with difficulty separated from it. 

 The mesocoria and metacoria, the membranes connecting the pro- 

 thorax and mesothorax and the mesothorax and metathorax, are 

 usually limited to the dorsal and lateral aspects and then only 

 marked as slight transverse constrictions. These coriae are effaced 

 without passing through a suture stage. The combined head and 

 thorax, as in the adult female of the Diaspidinae, are sometimes 

 designated as a cephalothorax. 



There is a strongly chitinized area extends dorsad and laterad 

 from the lateral margin of the proximal segment of each leg, a 

 coxa, in certain of the leg bearing species. This linear area has 

 been designated the episternum because it bears a projection for 

 the articulation of a coxa. This articular surface of each epis- 

 ternum is a coxacoila and the articular surface of the coxa which 

 is applied against the coxacoila is a coxartis. In those Hemiptera 

 where the pleural sclerites can be identified, the episternum is 

 usually large and forms the greater part of each pleural area, 

 while the epimeron is small and inconspicuous and forms a narrow 

 area along the caudal margin of the episternum or is covered b}'' it. 

 The coxacoila is typically formed from the episternum and epimeron 

 not only in the Hemiptera but in most insects, so that this area in 

 the Coccidae undoutedly contains a small portion of each of these 

 sclerites. For the sake of brevity, however, each of the entire 

 areas bearing a coxacoila has been called an episternum. This 

 sclerite is distinct in Icerya. 



Those species of coccids provided with an episternum are also 

 usually provided with an apodema. This is the thin, vertical, 

 cuticular plate extending into the body cavity from the inner 

 surface of each episternum. These pleural plates form a part of 

 the endoskeleton of the thorax, which is present in most insects, 

 but wanting in all legless coccids. This structure has no relation 

 to the notal area of the male, the mesoscutellum, to which the name 

 of apodema has been incorrectly applied. There is on each side 

 of the meson of the ventral aspect of each thoracic segment of 

 most insects a small invaginated lobe, a furca. The furcae also 

 constitute a part of the endoskeleton of the thorax. In the coccids 

 the furcae are present only in the generalized species and then are 

 represented only by small finger-like projections which are difficult 



