Dec, 1917.] Crampton : Abdominal Segments and Appendages. 229 



minal abdominal segments (and frequently the dorsal portion also) 

 is typically overlapped by a backward prolongation of the eighth 

 segment. Holmgren, 1909 (p. 150), states that the seventh abdom- 

 inal segment partially overlaps the following ones in the termites, 

 and in his fig. y;^ he designates this overlapping segment as the 

 seventh. I think, however, that he has mistaken the actual eighth 

 segment for the " seventh," due to the fact that the first abdominal 

 segment is not devloped ventrally, in the termites. The tenth segment 

 is moderately well developed tergally, but there is a tendency for the 

 suranale to become rudimentary, especially in the Blattids. When 

 the pygidium is developed (figs. 7 and 13) is usually projects down- 

 ward, instead of backward as in the Panorthoptera. The cerci vary 

 in form and in the number of segments composing them, but fre- 

 quently the basal segments are more annular in outline in this group. 

 The number of segments in the cerci may be reduced to one in this 

 superorder also (fig. 5), thus showing that the tendency toward the 

 reduction of the number of segments is quite widespread in all of the 

 insects here discussed, making it practically impossible to make any 

 general statements as to the number and character of the segments 

 of the cerci in the different groups. 



The Panplecoptera have apparently departed as little as any from 

 the ancestral condition of the lower Pterygota, and it is rather re- 

 markable that few if any of them seem to have retained any styli, 

 since the Lepismids and other related Apterygotan insects are pro- 

 vided with numerous styli (fig. 2, "st" and "m"), and these struc- 

 tures occur in the males of the other two groups here discussed. The 

 lack of an ovipositor in many representatives of the Panplecoptera is 

 another feature which might appear to argue against the primitive 

 character of this group, since a well-developed ovipositor occurs in 

 many Lepismids, and other related Apterygota. The very primitive 

 Apterygotan insects Campodea and Anajapyx, however, have no ovi- 

 positor, and the most primitive of all insects, the Protura, have no 

 styli either, so that the absence of ovipositor and styli in the Plecop- 

 tera, etc., may be regarded as a retention of a primitive condition, 

 rather than as a condition brought about by the loss of these struc- 

 tures. Furthermore, the development of the tenth abdominal seg- 

 ment ventrally, and the ring-like character of the ninth segment in 

 the Plecoptera (figs. 4 and 11) seem to be primitive characters, since 



