OF WASHINGTON, VOLUME XVI, 1914 59 



more or less united, separated by the triangular parasternum 

 (past) , from the sternellum (stl) , behind which is the poststernellum 

 (pstl). 



The line limiting the hypopleurite below, I call the hypopleural 

 line (hypl) and it is determined by perpendicular muscles running 

 from the posterior end of the antipleural suture (anti-hypl) . This 

 hypopleural line consists of two pieces. Below the anterior 

 piece lies the parasternum, below the posterior, the poststernellum. 

 The line separating the parasternum from the sternum I call the 

 sternal line (si) . This is determined by three long oblique muscles, 

 two from the superior cunea, just in front of the spiracle of the 

 following joint (s-st) and one (an-si) from the anterior cuneal 

 notch. The two first mentioned muscles are closely united at 

 their lower end in the Trogosita and Alaus larvae, while in Clerus 

 they are plainly separated (fig. 1, pi. III). The line limiting 

 poststernellum anteriorly against sternellum I call the postster- 

 nellar line (pstl) , and this is determined by a short oblique muscle 

 from the anterior cuneal notch (an-pstl). The other, anterior, 

 side of sternellum is defined by a line, the sternellar line (stl), 

 from the end of the anterior piece of the hypopleural line to the 

 posterior end of the sternal line. 



The study of the muscles, is as stated in the beginning, essential 

 to the correct understanding of these integumental parts. With- 

 out such a study it is well nigh impossible to interpret the struc- 

 ture of the surface in the more complicated cases. A few examples 

 will suffice to demonstrate this. In Alaus (fig. 8, pi. VI), the mus- 

 cles show that the first line below the pleural suture is but a branch 

 from the hypopleural line which is normally simple, and that the 

 hypopleurite, consequently, in this larval type consists of two 

 distinct pads, while in the other types this area is undivided. 

 Similarly, it could not have been recognized without muscle study 

 that the broken sternal line in Trogosita (fig. 5, pi. V), is identical 

 with the straight sternal line in Clerus (fig. 1, pi. IV), and Alaus, 

 a modification which makes the shape of the parasternum quite 

 different in these forms. 



In the above I have only mentioned the muscles, which have 

 a direct bearing on the formation of the various areas. There 

 are, however, a great many others, and a short account of these 

 may be useful in the identification and location of the leading 

 muscles, used in this paper. They are: 



(s-s). Longitudinal, bandlike dorsal, muscles in parallel series 

 immediately underneath the integument as far down as to the 

 spiracle; they run between a superior cunea in front and the 

 following superior cunea posteriorly (fig. 3). 



(i-i). Longitudinal, bandlike, ventral muscles in parallel series 



