148 THE BOOK OF NATURE STUDY 



the hairs, and is smaller. Take specimens of both crabs home 

 to the aquarium, where they can be readily kept, and watch the 

 habits of both. The most interesting point about the smaller 

 form is that though it usually climbs about weeds like a crab, 

 it possesses also the power of swimming like a lobster. The tail is 

 generally kept folded beneath the body like the tail of a crab, 

 but can upon occasion be straightened and bent, so that its 

 vigorous flapping propels the little creature through the water. 

 The most interesting point about the other and more sedentary 

 species, is the way it protects itself from particles of mud. We 

 have already emphasised the fact that most marine animals are 

 very sensitive to mud, deposits of which, especially on the gills, 

 are often rapidly fatal, for they prevent the proper action of 

 these organs. Now the hairy porcelain crab lives in muddy 

 pools, so that at first sight it would seem to be an entire exception 

 to this rule. A little observation will, however, show that the 

 object of its covering of hairs is to prevent the mud from reaching 

 sensitive parts of the body. In point of fact the little creature 

 spends most of its time over its toilet. Do not fail to notice 

 how the great fringe of hairs on the claws acts as a sieve to pre- 

 vent mud being swept into the gill chamber with the water of 

 respiration, how the rudimentary hind legs, with their terminal 

 brush of hairs, are used to clean out the posterior part of the 

 gill-chamber, how the feelers are periodically brushed and cleaned 

 by the hairy appendages near the mouth. If with a camel' s- 

 hair brush you try to clean the mud from the crab's hairs, to 

 make it a more presentable occupant of the aquarium, you will 

 find that the particles stick very closely, and a lens will show 

 that the reason is that the hairs are branched and serrated so as 

 to give them the maximum sifting action. 



Related to the porcelain crabs but more lobster-like in ap- 

 pearance is Galathea (G. squamifera), sometimes called the squat- 

 lobster. It is common in the rock pools, especially those near 

 low-tide mark, and reaches a length of about 3 inches. Do not 

 attempt to keep full-grown specimens in the aquarium, but 

 select a few small ones, often found in company with the small 

 porcelain crabs on the roots of oarweed. These small specimens 

 are often brilliantly coloured in blue and red, and their power 



