332 Mr Brindley, The proportions of the sexes 
he visited Rosevear in October 1912 the giant mallow (Lavatera 
arborea) was so high that a short man could walk hidden among ~ 
it. Armeria maritima is one of the commonest plants. Rosevear 
bears the ruined huts of the builders of the present Bishop Light- 
house, who inhabited it from 1850 to 1858. In 1912 and when 
he made a collection for me in September 1913 my boatman, 
Mr 8S. Jenkin, reported the islet swarming with earwigs. The 
specimens are nearly all large and the males conspicuously “high.” 
Among them is the longest pair of forceps which I have obtained 
or heard of, viz. 12°25 mm. ‘The Round Island collection of 1911 
contained one male with forceps 11:°0 mm. In Mr W. Bateson’s 
collection from the Farn Islands in 1892, by which he showed that 
the male earwig is dimorphic in respect of its forceps, the highest 
males have the value 9:0 mm.* 
The dimorphism of the male does not fall within the scope of 
the present paper; all that need be said is that in the Scilly 
Islands both “low” and “high” males occur, and that in some of 
the islands the “high” individual is strikingly in excess. The 
necessary measurements are as yet too incomplete for saying 
anything about the extent to which the two kinds of males are 
present in the Scilly Islands, and it should be borne in mind that 
the above notes on both the dimorphism of the forceps and the 
general size of body are from a comparatively superficial examina- 
tion of the collections. 
It is obvious that the Common Earwig is very abundant in 
the islands and that it exhibits well-marked local differences in 
respect of (a) numerical proportions of the sexes, (b) body size of 
adult, (c) percentage of “high” males. (6) and (c) naturally to 
some extent vary together: as pointed out by Bateson, the 
“high” male has a large body and the “low” male a small one, 
but the body dimensions give a monomorphic curve; the male 
earwig appears to be dimorphic only as regards its forceps. No 
explanation is at present forthcoming of the local variations 
mentioned above and we remain in the dark with regard to their 
causes as to those of local races in general. As remarked on p. 329, 
the percentage of males bears very slight or no relation to the 
mutual positions of the islands. Bryher and Tresco yielded collec- 
tions large enough to indicate the sex proportions with probable 
accuracy, the islands are contiguous and in both the male per- 
centage is high. On the other hand Samson, almost as near and 
separated from Bryher by very shoal water, has very few males. The 
estimate is based on a small total collection, but I am inclined 
to believe that the male percentage is really particularly low 
on this island, for we made it the object of prolonged search 
* Bateson and Brindley, Proc. Zool. Soc. Lond., Noy. 15, 1892, p. 585. 
