SUBFAMILY LECANIINAE 161 



also in position, in some species it is directed caudad and in others 

 dorsad. 



A structural feature equally as striking as the anal cleft is 

 the presence in the adult female of a triangular plate on each side 

 of the cephalic end of the anal cleft. These plates are adjacent, 

 exposed on the dorsum, and each plate is known as an operculum. 

 They are also known as the anal plates, valve anali, while Green 

 considered the two plates as a single structure and designated the 

 two together as the operculum or anal operculum and each of its 

 parts as an anal plate or valve of the operculum. The shape of 

 the opercula varies with the species. The angle at the caudal end 

 of each operculum is known as the apex, the one at the cephalic 

 end as the inner angle, and the one on the lateral margin as the 

 outer angle. The margin connecting the inner angle and the apex 

 is known as the mesal or inner margin, the one connecting the apex 

 and the outer angle as the caudo-lateral or outer margin, and 

 the one connecting the inner and outer angles as the cephalo-lateral 

 margin or base. Each operculum is attached to the body along the 

 lateral margin. The outer angle is wanting in semicircular 

 opercula and the base and outer margin form a continuous curve. 



The cuticle ventrad of the opercula in this subfamily is 

 invaginated and forms a barrel-shaped tubular structure or 

 eversible-sac continuous with the rectum. This is the "organo 

 retrattile anali" of Berlese and the anal tube of Thro and other 

 writers. As to just how this tube originated is not clear. A 

 similar result would be obtained if the anus and anal ring were to 

 migrate away from the exterior of the body, pushing the rectum 

 into the body cavity and pulling the portion of the cuticle sur- 

 rounding the anal ring into the depression formed to bound the 

 tube extending from the anal ring to the exterior. The anus is 

 located inside the body. It is surrounded by a distinct anal ring 

 which bears a varying number of anal ring setae, six, eight, ten, 

 or more, which project through the anal tube and when longer than 

 the anal tube may be observed projecting from its caudal end. 

 The anal ring usually bears prominent orbacerores. There are 

 two projections on the ental surface of the anal tube adjacent to 

 the anal ring to which large muscles are attached. These muscles 

 extend and retract the anal tube. They function also for extrud- 

 ing the excrement or honeydew and for everting the anal ring. 

 The surface of the cuticle lining the Ivimen of the anal tube is 

 finely longitudinally striated. These striations are frequently 



