MOMENTARY display by animals of conspicuous colours followed by reliance upon procrypsis has long been known. Jenner Weir (Trans. Ent. Soc. Lond., 22; 1869) directed attention to the conspicuous hind wings exhibited in flight by many otherwise cryptic moths and Oedipoda grasshoppers, and Lord Walsingham, in 1890 (Proc. Ent. Soc. Lond., 52; 1890), suggested that the sudden change when such flying insects came to rest serves to confuse the visual impressions of a pursuing enemy. H. B. Cott, in his work "Adaptive Coloration in Animals" (1940), devoted several pages and many figures to this 'flash coloration'. An interesting new example of the principle has been described in a letter from Staff-Sergeant J. E. Marson (6th (East Africa) Inf. Bde. Workshops, E.A.E.M.E., South-East Asia Command). "In Ceylon I have noted the effectiveness of the same principle as applied to certain species of spiders. The female of Herennia ornatissima (Doleschall) is a medium-sized spider, grey and brown above, with the underside of the abdomen and cephalothorax having brilliant yellow, orange or red markings, according to the maturity of the spider. It spins its web on rubber trees, from stumps of branches to the main trunk. The web is nine inches to a foot in length, and is very close to the trunk at all parts. The centre of the web is tubular and is fastened to the trunk by the tip of the tube. In this tubular depression, the female rests, almost perfectly camouflaged by the similarity of colour to the lichens which grow on the tree. If the spider is disturbed, however, a vivid red streak shoots down the trunk, as it jumps and lowers itself on a thread. The red streak stops as it alights further down the trunk with the underside of the abdomen covered. It is very difficult to follow the later part of this movement, owing to the rapid colour change. Many members of the Eresidœ, which retreat into their tube-like web endings when disturbed, jump when further attacked, and the same effect is produced by the highly coloured underside of the abdomen. It would appear that this colour change would once again offer protection against a foe attacking at close range."