72 Annals Entomological Society of America [Vol. IX, 



furcasternite (Fig. 4, pfsi). In Leuctra this sclerite is divided 

 longitudinally into two small sclerites. In Periplaneta the 

 fourth division or postfurcasternite, is probably represented 

 by two small sclerites on either side of and behind the fur- 

 casternite. (Fig. 3, pfsi). 



The spinasternite or fifth division is generally present and 

 usually quite small and variable in shape (Fig. 3, ss). It bears 

 a single internal apophyses, the spina, which is usually hollow. 

 This sclerite lies behind the postfurcasternite, when the latter 

 is present and behind the furcasternite when it is absent. 

 The spinasternite in some insects is free or attached to the 

 mesothoracic verasternite. In others it is either united or 

 fused with the furcasternite. It is so variable in position that 

 it is very hard to tell to which segment the spinasternite belongs, 

 but it probably belongs to the segment in front of it, as no 

 spinasternite has ever been described as occuring in front of the 

 prothoracic verasternite. In the prothorax of Corydalis, For- 

 ficula, etc., it is very small, being represented by the internal 

 apophyses only (Fig. 8, ssi). 



Audouin, '24, applied the term sternum to the entire ventral 

 surface of any thoracic segment. It has since been used to 

 designate various subdivisions of the sternum by different 

 authors and this has naturally led to some confusion. 



Mac Leay, '30, thought that each thoracic segment was 

 composed of four subsegments and hence assumed that the 

 sternum was composed of four subdivisions. He accordingly 

 proposed the terms praesternum, sternum, sternellum and 

 poststernellum for these supposed subdivisions. 



Newport, '39, adopted Mac Leay's views, but was unable to 

 find four subdivisions in the sternum of any living insect. 

 Mac Leay's terminology, however, has been used by several 

 writers. 



Crampton, '09, used the terms presternum, basisternum, 

 furcisternum, postfurcal sclerite and spinasternum, each sclerite 

 being named after some characteristic which it bears. I have 

 adopted this terminology in a slightly modified form, using 

 the prefixes (except "basi") with sternite, to denote the sub- 

 divisions of the sternum. 



Comstock and Kochi, '02, in their figures of the metathorax 

 of Pteronarcys and Stenopelmatus, have labeled the first abdom- 

 inal segment the "sternellum." In their figures of the neck 



