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IX. Note on the Manubrium of the Ninth Sternite in the 

 Male Earwig. By Malcolm Burr, D.Sc, F.E.S. 



[Read November 4th, 1914.] 



Plates XXX— XXXIII. 



An organ which has been almost totally neglected by 

 writers on the Dermaptera, whether taxonomists or 

 anatomists, is the Manubrium of the ninth sternite of the 

 male. The majority of authors, indeed, appear to be 

 totally ignorant of its existence. Verhoeff, it is true, 

 noticed its great length in the Psalinae, writing of this 

 group, in 1901, that " Subgenitalplatte des (^ vorne mit 

 recht langen endoskelettalem Fortsatz, der jederseits einen 

 Verdickungsfaden zeigt." Ten years later, Zacher figures 

 the incomplete manubrium of Anisolabis verhoeffi (1911, 

 fig. W^), but without comment. Jordan and Burr describe 

 it with a figure, in the case of Arixenia jacobsoni (fig. 14, 

 p. 403). Jordan refers to it as a special sclerite, it being 

 distinct from the ninth sternite in that group, and suggests 

 that its function may be that of a support to the penis. 

 This might be the case in Arixenia, where the organ in 

 question is short, transverse and so structurally strong, but 

 its great length and extreme narrowness in the Psalidae 

 deprive it of all rigidity. 



If we dissect out the ninth sternite of a male earwig, we 

 find on the basal, inner margin, an extension of the chitin, 

 consisting of a fine hyaline membrane supported by a 

 thread-like indurated chitinous frame. This is the 

 manubrium. In most groups it is short, rarely much 

 longer than broad, but it is extremely prominent in the 

 Psalinae. The acompanying photographs, for which I am 

 indebted to the Rev. F. D. Morice, illustrate the various 

 forms of this organ in sundry groups ; unfortunately, the 

 material has not always been of the best, the organ itself 

 being sometimes torn and distorted, or sometimes obscured 

 by bunches of torn muscular fibre which remain adhering 

 to the plate ; still, the illustrations illustrate the range 

 of variety in form and design of this organ in most of 

 the subfamilies of the Dermaptera. This diversity en- 

 courages us in the hope that from the manubrium we 

 shall be able to draw some very valuable characters. 



TRANS. ENT. SOC. LOND. 1915. — PARTS III, IV. (DEC.) 



