12 TRANSACTIONS LIVilRPOOL BIOLOGICAL SOCIETY. 



is its chance of escape, and very probably the habit of 

 lying quiet has been acquired for this purpose by the action 

 of natural selection. The ventral surface of the crab is 

 white, in marked contrast to the dark coloured back, and 

 ^his I believe is also protective. When stones are turned 

 over or shaken a certain number of crabs lose their hold 

 and fall on their backs. They then lie still with the white 

 ventral surface exposed and are readily mistaken for the white 

 worn fragments of shells an^ chips of rock found im- 

 bedded in the mud under such stones. 



Enlalia virldis is a Phyllodocean worm of a brilliant 

 green colour which is very common on the shore at 

 Puffin Island in the crevices of rocks and in the holes made 

 by Sii.ricava rugos<t, and is often seen hanging in a loose coil 

 or festoon from an overhanging ledge or from the under 

 surface of a stone. It is of course, when seen by itself 

 or when attention has been drawn Lo it, a conspicuous 

 object on account of its colour, but when lying upon green 

 seaweeds it is very effectually concealed. Very frequently, 

 however, the worm occurs amongst red and reddish-brown 

 seaweeds where it naturally forms a contrast with its 

 surroundings. In such cases it bears considerable resem- 

 blance to the tufts of the green filamentous Alga Cladophora 

 rupestris which are seen scattered about amongst the red 

 seaweeds. You may look at a tangled green bunch which 

 seems to be an Alga and wonder what it is that is slightly 

 unusual it its appearance, when perhaps one of the coils 

 will slowly move and the apparent seaweed resolves itself 

 before your eyes into a specimen of Enlalia. It is won- 

 derful how easily even the practised eye of a naturalist 

 may be deceived by these resemblances, and I have no 

 doubt it is the same with the eye of the careless fish or 

 other passing enemy. 



