36 PROCEEDINGS OF THE ACADEMY OF [Jan., 



and eucoxa), and is extended through the pedal region of the furci- 

 sternum (i.e., the "furcal suture") and up the other side of the insect. 

 With the "intertergal" space (between the postscutellum and the 

 remainder of the tergum) it may separate the segment into two rings, 

 but, from reasons previously given, it is not at all probable that this 

 indicates that the segment is double. 



Behind the furci-sternum (S' 3 ) in Nemura (pi. I) are two plates 

 (^pf) which may be termed the post-f ureal sclerites. These occur in 

 but few insects, and are relatively unimportant. 



The Spini-sternum. — Behind the furci-sternum is a smaller sternite, 

 which bears an internal unpaired apophysis, the "spina," and may 

 hence be termed the spini-sternum. This sclerite varies greatly in size 

 and shape, and is never very large. 



The prothoracic spini-sternum is the most constant, and occurs in a 

 large number of insects. In the Blattidse (pi. Ill, £' 4 ) it is very long 

 and narrow, while the prothoracic spini-sternum of Nemura (pi. I, 

 S\) is drawn out transversely into two wing-like processes. In the 

 Trichoptera (fig. 18, S\) and Xyelidse it is very small, and in many 

 insects it is represented only by the endoskeletal "spina" or unpaired 

 pophysis. 



The prothoracic spini-sternum (pi. Ill, S' 4 ) usually lies just in front 

 <of the basi-sternum of the mesothorax, being much nearer to the meso- 

 thorax than to the prothorax. Again, in certain insects (Corydalis 

 for example) the mesothoracic spini-sternum is united with the meta- 

 thorax, but in each case the musculature clearly indicates to which 

 segment the sclerite in question belongs. 



In the Blattidae (pi. Ill, S'" 4 ) the metathoracic spini-sternum is a 

 distinct sclerite, but in Nemura (pi. I, £'" 4 ) it is united with the furci- 

 sternum, and in most insects it is indistinguishably fused with the 

 latter sternite. As has been mentioned, the prsesternum is usually 

 fused with the basi-sternum (except in a few insects such as Nemura, 

 Ectobia, etc.) and the spini-sternum frequently lies directly in front of 

 the basi-sternum. On this account it would seem very probable that 

 Meinert's, '67, prsesternum corresponds to the spini-sternum, rather 

 than the prsesternum of Comstock, '02, and the writer. This, however, 

 is mere supposition, and cannot be determined until specimens of 

 Japyx can be obtained for dissection. 



Amans, '85, divides the sternum into two regions, the ante- and post- 

 sternum. The former of these two regions may possibly correspond 

 to the prse- and basi-sternum, and the latter to the furci- and spini- 

 sternum, but it is impossible to determine this from Amans' descrip- 



