180 Dr. H. Schaum on the Composition of the Head, 



In the male oi Forficula gigantea, and allied species, there are 

 also nine dorsal segments (PL VI. rig. v. 1-9), a lamina supra- 

 analis (c), which attains here a great size, a pair of forceps ana- 

 logous to the style (d), and eight ventral segments; while in the 

 female there are but seven dorsal and six ventral segments con- 

 spicuous externally. The lamina supraanalis has in this case 

 been counted by Prof. Westwood, in a paper on the external 

 anatomy of Forficula (Trans. Ent. Soc. i. p. 157, pi. 16. fig. 6), 

 as the ninth dorsal segment of the male, because he erroneously 

 considered the first abdominal segment (fig. v. 1 & fig. vi. 1) as 

 a part of the mctathorax (m), believing that it might thus be 

 proved that in Forficula at least the metathorax is provided with 

 a pair of spiracles (which is, however, nowhere the case). There 

 can be no doubt as to the nature of the part in the apterous genus 

 Chelidura corresponding to this in the Forficula. It fills there 

 the posterior sinus of the metathorax, being quite separated from 

 the latter, and covered at its sides by the produced angles of it, 

 beneath which the stigmata of the first segment are concealed. 



In all these insects, as in all those undergoing a complete 

 metamorphosis, the number of ventral half-segments is less than 

 that of the dorsal ones, being eight in the male and seven in 

 the female of both Locusta and Pachytylus, and being also eight 

 in the male of Forficula*; and it is, as in the holometabolous 

 insects, the first dorsal arcus which has no corresponding ventral 

 arcus. 



There remains, however, one group of insects in which, ac- 

 cording to the general opinion, ten segments of the abdomen, 

 both the dorsal and ventral half-segments, are fully developed, 



view, which, however, could only be proved in that way. Observations 

 on the pupa? of Coleoptera led Erichson to the conclusion that the horny 

 parts of the genital organs are not modifications of the last segments, but 

 are developed independently of them (Erichson, Archiv, 1848, ii. p. 62). 

 In trying to prove his thesis by the composition of those organs in perfect 

 insects, M. Lacaze Duthiers starts from a theoretical axiom, that each seg- 

 ment of insects is normally composed of six parts — three tergal ones (one 

 tergum and two epimera) and three sternal ones (one sternum and two 

 episterna), — and that it bears a pair of tergal and sternal appendages, called 

 by him " tergorhabdites " and " stemorhabdites." lie then refers the parts 

 composing the genital organs to the tergum or epimera, or sternum or 

 episterna, or tergorhabdites or stemorhabdites of the ninth abdominal seg- 

 ment. It is, however, only in the wing-bearing segments that six parts 

 can be really distinguished, and that tergal appendages exist; and here the 

 epimera are sternal, and not tergal parts, like the pieces designated by 

 M. Lacaze Duthiers the epimera of the ninth segment. 



* By a mistake which I cannot explain, Prof. Westwood, in his paper on 

 Forficula (I. c. pi. 16. fig. 6), figures the metasternum (PI. VI. fig. v. m). to 

 which the posterior legs are attached, as the first ventral segment of the 

 abdomen, and thus enumerates nine ventral segments. 



