PROC. ENT. SOC. WASH., VOL. 20, NO. 3, MAR., 1918 43 



The sixth sternal plate is the spinastermte, or spinasternum 

 (fig. 14, ss) which, as the name indicates, bears the spina, or in- 

 ternal median unpaired apophysis for muscle attachment. The 

 location of the spina is indicated externally by the spinal pit 

 (figs. 3, 5, etc., s). In many instances in which the spinasternal 

 region is not chitinized, the spina is present, and to it are attached 

 the characteristic muscles. The spino-furcal muscles extend 

 between the spina and the furca of the same segment, and the 

 coxo-spinal muscles extend between the coxa and the spina of 

 the same segment; while the prospino-mesofurcal muscles extend 

 between the prothoracic spina and the mesothoracic furca, and 

 the mesospino-metafurcal muscles connect the mesothoracic spina 

 with the metathoracic furca. Similarly, the mesocoxo-prospinal 

 muscles connect the mesothoracic coxae with the prothoracic spina, 

 and the metacoxo-mesospinal muscles connect the coxae of the 

 metathorax with the spina of the mesothorax. In Periplaneta, 

 the interspinal muscles connect the spina of one segment with 

 that of the segment following it. When the muscles are retained, 

 they serve to assist in homologizing the regions in question, , even 

 when the latter are not pigmented and strongly chitinized. 



The spinasternum (figs. 4, 6, 7, etc.) is usually situated between 

 the subspiracular plates ip, or between the subspiracular regions; 

 but, in all probability, the spinasternum belongs to the segment 

 in front of it, while the subspiracular plates belong to the segment 

 behind them, since the spiracle develops in the segment behind 

 it, and later migrates into the intersegmental region, or even 

 into the posterior portion of the segment in front of it, as in the 

 prothorax. On the other hand, it is quite possible that the 

 spinasternum, instead of being the posterior most sternite of the 

 segment in front of it, may be the anteriormost sternite of the seg- 

 ment behind it, since the musculature would easily admit of 

 such an interpretation, and in certain cases, such as in the pro- 

 thoracic sclerites of Japyx, there is some reason for considering 

 that the anteriormost prosternal plate may be homologous with 

 the spinasternum. This point, however, can be best determined 

 by an embryological study of the region in question, and for the 

 time being, I would consider . the spinasternum as the posterior 

 most sternal subdivision. 



Other Terminologies and Interpretations. 



In the Diplopod Julux, and the Crustacean S'/i/ilf<i (which 

 at that time were classed as "insects"), McLeay, 1830, thought 

 that he could detect four sub-segments in 'each typical segment. 

 Since the prescutal, scutal, scutrllar, and postscutellar areas 

 had been noted in the tergum of true insects, Aid. cay erroneously 

 concluded that these four areas represent the terga of four sub- 



