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NOTE ON A CURIOUS FACULTY IN SPIDERS. 
Rev. O. PICKARD-CAMBRIDGE, M.A., F.R.S. 
Wareham. 
In the ‘Naturalist’ for November, 1906, No. 598, p. 401, Mr. 
W. W. Strickland (Singapore) gives an account of two spiders 
of the family Sa/ticide, in whose fore-central eyes he noticed a 
change from one colour to another, ‘evidently under the control 
of the spider’s will.’ Being unable to account for this, and the 
Curator of the Singapore Museum being equally ignorant of 
such a faculty in spiders, Mr. Strickland tells us that he wrote 
to Mr. R. I. Pocock, giving an account of this wonderful faculty, 
and he (Mr. Pocock) replied, saying that the faculty ‘ was quite 
unknown to naturalists.’ Will you allow me to point out that 
such a faculty is not quite unknown to naturalists. The late 
Mr. John Blackwall, whose researches on Araneology were 
extensive, and are well known, writes (Annals and Mag. Nat. 
Hist., Pt. 1, Vol. XVIII, No. 120, p. 299) where he is 
speaking of one of the Zhomzstde (Thomisus—now Oxyptila), 
pallidus, ‘this species, with Thomzsus cristatus, Thomisus 
bifasctatus, and some others, has the power of changing the 
colour of the anterior intermediate pair of eyes from dark red- 
brown to pale golden-yellow by a very perceptible gnhternal 
motion. No such motion appears to occur in the other eyes, 
which are always black.’ Mr. Blackwall has also, I believe, 
noticed this faculty in some other publication, to which I am 
unable at this moment to give the reference. I may add, how- 
ever, that I have on many occasions noticed similar changes, 
but. always in my experience in some spider of the family 
Salticide. The only doubt I had was about the ‘faculty,’ 
whether the phenomenon was produced at the will of the 
spider, or whether it was simply caused by a movement, very 
slight perhaps, and almost imperceptible at times, of the spiders 
caput, occasioning, of course, the light to fall upon the convex 
transparent cornea of the eye at a different angle, and so reflect- 
ing a different light within the eye. The internal variation in 
colour, however caused, is very noticeable in some at any rate, 
perhaps in all of the Sad¢éicid@; 1 have observed it especially 
in one, a tolerably common species, Hasarius falcatus Clerck 
(Salctcus coronatus Blackw). In an adult male example of 
this spider, examined not very long ago (which had been in 
spirit for over nine months), the large fore-central pair of eyes 
was as transparent and as brilliant as if the spider were still 
alive ; and certainly in this dead spider there was a change of 
3go7 January I. 
