134 Annals Entomological Society of America [Vol. XI, 



4. Somite Eleven. — Somite eleven, as has been shown in 

 the tables, occurs the most infrequently of any of the four 

 caudal somites studied. It is the most characteristic of the 

 Orthoptera of any order, although it also occurs in certain gen- 

 eralized families. When present it is posterior to the tenth, 

 surrounds the anus, and is membranous except in such forms 

 as the female grasshopper, where its tergum is highly chitinized, 

 and clearly separated from the tenth tergum by a well-marked 

 suture. Posterior to it in those cases, in the adult, lies the 

 so-called twelfth somite of Heymons showing in both Dissosteira 

 and Melanoplus (Plate VI, Figs. 9 and 10; 1, 10, 13, and 17, tl2) 

 very distinct in the female. This suture is not, however, present 

 in certain nymphal stages, according to many investigators, 

 even when it appears in the adult, and it would seem, therefore, 

 to be a secondary modification. In other orders than the 

 Orthoptera the eleventh somite is a short, homogeneous, mem- 

 branous ring surrounding the anus, often distinguishable with 

 difficulty from the anal lobes. 



5. General Statement. — Of the four somites considered 

 above, it is evident that the ninth is the most specialized of all, 

 both by reduction of parts, by modification of form, and by 

 lack of chitinization — all three characteristics following upon 

 retraction of the caudal end of the abdomen. Somite eight 

 changes least from its form in the primitive type, and in the 

 generalized Orthoptera, somites ten and eleven become the 

 simplest in form, structure and substance, by specialization and 

 reduction of parts. 



6. Appendage I. — This appendage occupies the most 

 extreme ventro-caudal position, and shows its real connection 

 with somite eight only in the saw-flies and wasps. This pair of 

 appendages usually seems to be placed closely adjoining the 

 ninth sternum, and is often referred to as the ventral pair of 

 appendages. The ventral pair of ovipositors of the grasshopper 

 (Plates V and VI) show this relative position, although the 

 connection would appear at first glance to be with the eighth. 

 This is also true in Appendage I in the female Lepisma. This 

 appendage belongs to the eighth somite, but is often crowded 

 out of its typical position by the shape, retraction, and function 

 of the caudal somites. The Hymenoptera present another and 

 one of the clearest cases of the relation between Appendage I 



