132 Annals Entomological Society of America [Vol. XI, 



insects, with incomplete metamorphosis, the ninth somite shows 

 speciaHzation in the sterum, which, early in its history in the 

 female cockroach and grasshopper, is much smaller and far 

 more variable in shape than the tergum. In the Hemiptera it is 

 a larger, less modified somite, in the sternum as well as in the 

 tergum, and this continues to be true in Corydalis and Panorpa, 

 although it is longer in proportion to its width than before, this 

 latter characteristic following out the general shape of the 

 scorpion fly. In the Coleoptera the entire somite consists of 

 most irregularly shaped chitinous sclerites, and, in large pro- 

 portion, of cuticular, non-chitinized membrane. Such sclerites 

 may not be bilaterally placed with reference to the shape of the 

 beetle, but in a direct ventral view only a" part of the sternum 

 will show, and that, irregular in shape, as in Hydrophilus 

 (Plate XIII). In the Lepidoptera the ninth somite is often a 

 homogeneous, membranous cylinder as in the females of 

 Phlegethontius and Pryonoxyatus ; or, as in the male of the 

 same genus there may be a slender, curved sclerite bilaterally 

 placed in a broad area of membrane; or, as is true of Hepialus 

 the sclerites may be broad and short, more highly chitinized 

 than the succeeding somites. In the Diptera it varies from the 

 small, crescent-shaped sternum of the female Tipiila abdom- 

 inalis, to the broad, well-rounded tergum of the male in the 

 same species. 



Between these two extremes, one finds every irregularity, of 

 size and shape, as is well illustrated by the long, sub-cylindrical 

 somite of the male blow-fly and the irregularly chitinized, 

 largely membranous sternum of the female of the tabanid. The 

 corresponding sclerite in the male further accentuates the shape 

 found in the female so that it is almost forked, the points pro- 

 jecting posteriorly and, in the female blow-fly we meet with an 

 almost typical ninth sternum, its only variation being a some- 

 what curved caudal margin. 



The ninth sternum is highly specialized in shape and arrange- 

 ment in the Hymenoptera, after the same manner already com- 

 mented upon in connection with the eighth, and it consists of 

 two irregular sclerites again somewhat approaching a triangular 

 shape. However, just as plainly marked as in the case of the 

 eighth, is the primitive connection of this sternite with its 

 respective pair of appendages: a most generalized point in a 

 highly specialized group. It should also be noted that this 



