THE ABDOMEN. Ill 



project as lappets (ab. lobatum), or rise in thorns or spines from the 

 surface of the plates. If a solitary large horn be placed upon the 

 centre of the venter, it is called HASTATE (ab. haslatum) ; HORNED 

 (ab. cornutum), on the contrary, when it proceeds from the back ; 

 MARGINATE (ab. marginatum), when its sides project in sharp ridges, 

 (Coreus marginatus} ; or winged (ab. (datum), when the projection of 

 the margin is very considerable (Coreus quadratus, many Ting-is). 

 These differences of margin are generally found only in such insects 

 whose superior wings form horny wing-cases; consequently only among 

 the Coleoptera, although among these but rarely, Orthoptera and 

 Heiniptera, and among the latter most frequently. 



85. 



We must now turn our attention to the abdominal appendages. 



The appendages of the abdomen may be classed into three large 

 groups, according to whether they belong to the anus or the sexual 

 organs, or to neither one nor the other. 



The ANUS is a round opening near the upper side of the last abdominal 

 segment, and is in but few instances provided with peculiar appendages, 

 but lies within the last abdominal segment which closes the rectum 

 with its two halves. In these cases, the sexual organs open into the 

 cavity formed by the last segment, and are similarly covered by it. It 

 might not, therefore, be inappropriate to call this cavity with its opening 

 by the name applied to the analogous construction in Birds, the CLOACA. 

 Kirby and Spence propose podex as the name for the superior flap, and 

 for the lower one, hypopygium. In those instances in which the anus 

 is not closed by the flaps of the last segment of the abdomen, we 

 observe peculiar thick processes which close its aperture like the prongs 

 of tongs ; they are sometimes hooked, and are then called UNCI 

 (Locusia, Gryllus). 



The appendages attached to the sexual organs are more remarkable 

 both in shape and function. 



With respect to those upon the anal segment of male insects, 

 they are generally less peculiar than those of females. Both sexes 

 are deficient in these appendages when the last segment forms a 

 cloaca; on the contrary, we find in those which have a free sexual 

 opening a sort of tongs close to the male organ, between the prongs of 

 which the penis is found, either lying freely exserted, or else retracted 



