60 [Maroh. 



at its base which is characteristic of the male. As Dr. Malcolm Bm-r 

 points out ("Fauna of British India: Dermaptera," 1910, p. 9), "Such 

 cases are frequenth" recorded as hermaphrodites, but whenever the full 

 complement of nine segments occurs together with one male branch, it is 

 more probable that these are not gynandromorphic specimens, but merel}'^ 

 that one branch has been unable to obtain full development." Mutila- 

 tion or insutficient nom'ishment may account for retarding the normal 

 development of a forceps, so that in the imago it presents the characters 

 of a nymph's forceps, for, on the whole, these " female " forcipes in males 

 resemble those of n3^mphs as much as they do those of adult females. 



The instance now described and illustrated is of a different kind, as it 

 is one of the forcipes (the right) bearing two branches on its outer side, 

 which give it an antler-like appearance. Its length 

 is 3"25 mm., while that of the left or normal forceps 

 is 3 '75 mm. Whether the difference in length and 

 the bluntness of the extremity and branches of the 

 right forceps were due to insufficient nourishment 

 during development or to subsequent injury is, of 

 course, uncertain, but it \vill be noticed that the 

 organ is abnormal also in the elongated and non- 

 serrated condition of the chamcteristic inner 

 Brownsea c? , 1911. , . , 



shoulder. 



The specimen occurred among a batch of 353 adults of both sexes 

 collected on Maryland Farm, Brownsea, the largest island in Poole 

 Harbour, in 1911. Other collections from the same spot, made in 1910, 

 1912, and 1913, produced no abnormalities in forcipes beyond the so- 

 called " female " forceps of males which are met with in collections from 

 any locality. 



This antler-like forceps does not observe any rules of symmetry such 

 as are set forth by Bateson (" Materials for the Study of Variation," 

 1894, chaps, xx-xxii) in dealing with duplicity and other forms of 

 branching in the appendages of insects and crustaceans. The abnormal 

 forceps seemed to have been no disadvantage to its possessor, which was 

 of healthy appearance ; and the same may be said, in general, of males 

 with "female" forcipes. 



I am indebted to Miss Maud D. Haviland, H.M.B.O.U., for kindly 

 making the above camera lucida drawing of the Brownsea specimen. 



Zoological Laboratory, Cambridge. 

 February, 1918. 



