3H THE PLACE OF MIMICRY 



A good example is to be found in the little British 

 crab Hyas coarctata*, which covers itself very com- 

 pletely with Algae, exposing only the pearly pink large 

 claws. It then climbs into a mass of Alga, to which it 

 imparts a gentle swaying motion. The attention of small 

 fish is probably first attracted by the movement, and their 

 interest excited by the brightly coloured claws which alone 

 can be seen. They approach to within striking distance, 

 are seized and devoured by the crab. All this has been 

 observed in the aquarium by Prof. A. F. Dixon, of Dublin, 

 to whom I am indebted for the information. 1 The Hyas 

 itself is greedily devoured by larger fish, and it cannot 

 be doubted that the adventitious covering acts as a 

 defence against these enemies. This crab affords a good 

 example of the complexity of the uses of colour. The 

 covering of Algae is an alloprocryptic defence against 

 enemies, an allanticryptic assistance in the capture of 

 prey, a capture also aided by the alluring or pseudepi- 

 sematic colouring of the claws. 



A subtle form of allocryptic defence is found in the 

 use of the colour of the food in the digestive organs 

 showing through a transparent body, or the still more 

 remarkable cases in which it is dissolved in the blood 

 and secreted in the superficial cells of the body. In one 

 case it has even been shown that the different shades of 

 green produced by modified chlorophyll from the leaves 

 of different plants, is preserved in the pupa, collected into 

 the eggs of the perfect insect, and can still be detected in 

 the larvae of the next generation when first hatched from 

 those eggs. 2 



True or Batesian Mimicry is closely related to the 

 Cryptic Colours described and illustrated above, but 

 differs in that the mimetic animal resembles an object 



1 On the Marine Invertebrate Fauna near Dublin, by G. Y. and A. F. 

 Dixon. Proc. Roy. Irish Acad t , 3rd ser., vol. ii, no. 1, 1891, p. 30. 



2 Smerinthus ocellatus. See Proc. Physiol. Soc. in Journ. Physiol, 

 vol. viii, 1887, pp., xxv, xxvi. The fact that modified chlorophyll derived 

 from food forms an important element in the colouring of certain larvae 

 has been clearly proved in the case of Tryphaena pronuba. See Proc. 

 Roy. Soc, vol. liv, 1893, P' 4*7, pi- 3» 4- 



