a Family of Thysanura. 371 



of greater consistency than any of the others ; the colour is a 

 dark yellowish brown, even in young individuals^ where the rest 

 of the body, or at any rate the greater part of it, is milk-white. 

 The general shape is prismatic, and the section tolerably rect- 

 angular, the sides being formed by the perpendicular pleural 

 shields, so that the skin connecting them with the ventral and 

 dorsal shields does not appear in view. Connected with the 

 dorsal shield of this segment, in the middle of its posterior 

 margin, we observe the small, short and broad anal plate, under 

 which the anus is situated. With regard to the term anal plate 

 {lamina analis), I refer to my paper on Forficula^ : it is the 

 same as L. Duthiers^s endecato tergite; but I see no reason for 

 interpreting it as the remains of an eleventh ring; and it has, 

 of course, nothing to do with the entirely superfluous term 

 lamina supra-analis, which is sometimes applied to the tenth 

 dorsal shield in Ulonata. 



Comparing the structure of the posterior part of the abdomen 

 in Campodea and Forjicula, the matter stands thus : — In Cam- 

 podea all ten abdomen-rings are perfectly and equally developed; 

 in Japyx the requirements of the forceps cause a dispropor- 

 tionate development of the tenth ring, whilst the ninth is some- 

 what reduced and its ventral shield divided into two triangular 

 plates. In both these genera the anus opens at the extremity 

 of the abdomen. In Forjicula there are also ten distinct abdo- 

 men-rings, of which the first (segmentum mediale), as in most 

 insects, is closely connected with the thorax ; here, too, the last 

 or tenth ring is disproportionately large; but whilst in Japyx 

 the dorsal and ventral shields are about equally developed, the 

 dorsal shield preponderates very much in Forjicula, the anal 

 plate is proportionally larger, the ventral shield divided into 

 two triangular plates, and the anus is drawn back from the ex- 

 tremity of the body, and opens at the root of the tenth ring, 

 instead of at its apex, between the two halves of the tenth ventral 

 shield. Besides, the eighth and ninth rings are almost rudi- 

 mentary in the female Fo?]ficula. 



The short but powerful hooked branches of the forceps of 

 Japyx possess regular condyles and corresponding sockets both 

 in the ventral and in the dorsal shield, just as in Forjicula; but 

 I am unable to say with certainty whether the forceps present 

 sexual differences, as is the case in Forjicula, as I have not been 

 able to sacrifice a sufficient number of individuals for dissection, 

 but I do not consider it probable. The spiracles are situated in 

 the side folds of the first ten rings. 

 * The ganglia of the nervous system ai'c large and round ; each 



* Nat. Tidsskrift, 3 ser. vol. ii. p. 446. [Comp. Ann. & Mag. Nat. Hist, 

 ser. 3. vol. xv. p. 484. — Translator's note.'] 



25* 



