MIMICRY. 535 



has left the door open behind it."* It may be contended that 

 this shows only mimicry in the habitation, and not in the appear- 

 ance of the animal itself; or, again, that "aggressive" rather 

 than " active " should be the qualitative term applied to this 

 mimicry ; but we can refer to instances where animals disguise 

 their own bodies in a similar manner, and with a like intelligence, 

 to these Spiders. The little iEsop's Prawns (Hippolyte (virbius) 

 varians. Leach, and H. fascigera, Gosse) may perhaps be cited as 

 practisers of active mimicry. Prof. Herdman, in 1*93, described 

 four variations of H. varians, each agreeing in hue with the 

 colour of its special habitat,! and was inclined to accept the 

 fourth possibility of explanation which he suggested, viz. " The 

 young may be very variable in tint, and then, by the action of 

 natural selection, such as do not agree in hue with the surround- 

 ings will be eliminated." Mr. James Hornell, at the Jersey 

 Biological Station, has made a further series of experiments with 

 these species, and has accepted the third postulate of Prof. Herd- 

 man, viz. the " adaptability may be retained throughout the rest 

 of their lives, and the adults may change hue upon change of 

 environment." Mr. Hornell found that a pale olive-brown 

 H. varians taken from amid similarly coloured seaweed became 

 of a vivid green within an hour when placed with Enteromorpha, 

 and the same specimen changed to a pinkish red within three 

 hours when placed amid Delesseria. Again, red-coloured speci- 

 mens of the same species from amongst tufts of red weeds 

 changed to green during a single night when placed with Entero- 

 morpha. or with Cladophora, and back again to red within four 

 hours when placed once more amid red weed. This change of 

 hue took place as rapidly in the dark as in the light. The weeds 

 affected by the smooth -skinned H. varians, in the great majority 

 of cases, are smooth in surface, and not overgrown with foreign 

 matter. " In marked contrast, the body of H. fascigera is orna- 

 mented with tufts of brush-like hairs, and if a spray of the coarse 

 Corallina, where this species makes its home, is examined, the 

 stems are found covered with a multitude of abodes of tiny 

 " messmates," porcelain-like coils of the little tube-worm Spirobis, 

 dull-looking cylinders tenanted by that lovely miniature Sabeliid, 



* ' Pop. Account Travels in S. Africa,' p. 221. 



f ' Sixth Annual Report of the Liverpool Marine Biology Committee.' 



