THE CRUSTACEA 121 



which the young develop, just as in the " Opossum 

 Shrimps " (Mysis), which we shall consider presently. 



The species represented on our coast are Caprella linearis, 

 in which the body is uniformly linear, and Caprella acanthi- 

 fera, in which each segment of the body is produced into a 

 point on the dorsal aspect. 



They are very pugnacious, and the males fight desperately. 



The Isopoda (" Equal-footed "). This sub-order has for 

 its type the common wood-louse of our gardens. It also is 

 very strongly represented on our shores. The most familiar 

 example on the coast is Lygia oceanica. This is about an inch 

 and a half long by half-an-inch wide, and rather flat. The 

 colour is green, with black and white spots and mottlings. 

 It is very abundant, and at dusk can be seen scuttling 

 rapidly over rocks and sea-walls just above high-tide 

 margin. This, like the sand-hopper, seems to be a marine 

 form taking to a land existence. 



In the cracks of rocks in places which the tide covers, 

 and also under loose stones in rocky hollows, but still high 

 up in tide range, may be seen, often in great colonies, a 

 form which rolls itself up into a ball, like the " pill wood- 

 louse " of our gardens. This is Sphceroma serratum. It 

 is about half-an-inch long, by nearly as much in width 

 and very convex. Its colour varies : some are red, others 

 yellow, white, and green, but the majority are speckled 

 pink and white. 



There are several species of Sphceroma, and other genera 

 closely allied to them. Nicea bidentata is a common little 

 one in dry places and is remarkable for two spinous processes 

 on one of its segments which projects when it rolls itself up. 



Some of the Isopoda are parasitic on fishes, others on 

 crustaceans (see Fig. 47). 



The large Mga, about the size of a cockchafer, attacks 

 the cod chiefly. A beautiful species, of rather smaller size, 

 is named Anilocra Mediterranea. This one is common in 



