CRUSTACEA OF THE SEASHORE 115 



day ; but the valves which close the opening of the 



shell fit so tightly that a little sea-water is enclosed, 



and the animal is protected from drying up even when 



exposed to the heat of the sun. If a stone or a chip 



of rock, with a few of these animals on it, be placed 



in a jar of sea-water, their peculiar mode of obtaining 



food can easily be watched. The valves will presently 



be seen to open a little, and the curled cirri will be 



protruded, opened out like the fingers of a hand, 



and withdrawn again with a sort of grasping motion. 



These movements are continued without stopping 



while the animal is under water. If the cirri be 



examined with a pocket-lens or under a microscope, 



it will be seen that they are fringed with stiff bristles, 



so that, when they are opened out, the whole forms 



a kind of *' casting-net." As it is swept through the 



water, this net entangles minute floating particles of 



animal or vegetable matter, and carries them into 



the shell, so that they can be seized by the jaws and 



swallowed. The cirri, as we have already seen, are 



really the modified thoracic limbs, so that, in Huxley's 



words, " A Barnacle may be said to be a Crustacean 



fixed by its head, and kicking the food into its 



mouth with its legs." 



A mode of obtaining food by " net-fishing," not 

 unlike that employed by the Barnacles, is found in 

 certain Crustacea belonging to a widely different 

 group — the little ''Porcelain Crabs" (Fig. 41) 

 mentioned above. Mr. Gosse observed that the 



