THE CANADIAN ENTOMOLOGIST. 



185 



The xii and xiii segments are always greatly modified and intimately 

 connected with the sexual system. The chitinous covering of the xii 

 segment is much thicker than in the preceding ones, and forms a closed 

 ring about the body. In the lowest families (Micropteryginse) this ring is 

 of equal breadth all round, but in the majority of the remaining families 

 the dorsal portion is much more broadly developed than the ventral and 

 lateral portions, the whole bearing a striking resemblance to a signet ring. 

 In many cases, examples of which can be found in every group with the 

 exception of the Rhopalocera, a lateral joint is present, dividing the ring 

 into a ventral and dorsal portion. 



To the median ventral portion of the wing is attached the Saccus, a 

 secondary invagination of the intersegmental membrane, which projects as 

 a strongly chitinized pocket more or less deeply into the abdomen. In 

 several species of Bombycidcp. considerable modification of the Saccus has 

 taken place, leading in extreme cases to the formation of a large chitinous 

 sac beneath the sexual organs (Bombyx rubi). In but few instances is the 

 Sacctis completely lacking. 



The conical anal segment (xiii) is scarcely visible in the majority of 

 cases in the fully developed organ. The Uncus and Scaphiuvi^ which 



