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



nearly represent the original one, while the sclerites of the higher 

 forms, such as those shown in figures 17, 20, and 23, present 

 some variants of the original condition, as might be expected. 

 In figures 20 and 23, the dorsal plates labeled b form the apical 

 tergal plates, while the plate labeled c is the lateral tergal plate. 

 In figure 17, the plate labeled a is apparently an additional an- 

 terior dorsal tergal plate of the mesonotum, and the plates labeled 

 c appear to be additional upper and lower anterior and posterior 

 lateral tergal plates. 



Intersegmental Region. 



In figures 18, 21, etc., there occurs an intersegmental region 

 labeled int, in which the spiracle sp is located. In some instances, 

 a subspiracular plate (fig. 21, ip) occurs below the spiracle. These 

 plates are not always associated with the spiracle (fig. 12, ip), and 

 are apparently homologous with the inter pleurites, which, in the 

 neck region, form the lateral cervical plates (figs. 23, 24, 16, 17, 

 etc., Ic), while the other intersegmental plates form the dorsal 

 and ventral cervicals, as has been discussed in a recent article 

 (Crampton, 1917 a). 



An examination of figures 23, 20, 17, etc., would lead one to 

 believe that the first spiracle (fig. 23, sp) is prothoracic, since it is 

 apparently located in the prothoracic region. Embryology, 

 however, shows that the spiracle originates in the anterior portion 

 of the segment behind it, and later appears to migrate to an inter- 

 segmental position, or even into the posterior region of the seg- 

 ment in front of it. In such cases, there is frequently an impressed 

 line, or fold, in front of the spiracle, marking it off from the 

 remainder of the segment in front of it, although this is not 

 always the case. 



The intersegmental region (figs. 18, 21, etc., int) is doubtless a 

 demarked region of the segment behind it, although a portion of it 

 may belong to the segment s in front. The spinasternite (figs. 7, 6, 4, 

 etc., ss) for example, is located between the intersegmental plates 

 ip near the spiracles; but, while the spiracles belong to the seg- 

 ment behind them, the spinasternite has been provisionally 

 regarded as the posteriormost sternal subdivision of the segment 

 in front of it. The spinasternum itself, however, may possibly 

 belong to the segment behind it also, since- the musculature 

 would permit of such an interpretation; but, unti. an embryologi- 

 cal study of the region in question has been made, it is impossible 

 to determine this point. 



The dorsal intersegmental plates it of figure 18 appear to lie 

 homologous with the interterbites of the adult insect. Their 

 exact significance, however, is not clear, and until an embryological 



