202 CRUSTACEA. PART in. 



The Amphithose enclose themselves in a cylindrical tube 

 open at both ends. The animal is very active, running 

 along the branches of the sea-weeds by means of its an- 

 tennae instead of its feet, which remain within the tube. 

 In general only the first pair of antennae are put out to 

 catch prey. If the animal be prevented from advancing, 

 it immediately turns its body within the tube, and pro- 

 trudes its head from the other extremity. 



Is op o da. 



The order of Isopoda are so called because of the 

 sharp -and equal claws of their walking feet, which 

 are often prehensile. Their body is short and flat- 

 tened, and their small head is almost always distinct 

 from the throat. They are very numerous, and are di- 

 vided into walking, swimming, and sedentary animals ; 

 the females have horny plates on some of their feet, 

 which fold under the throat and form a pouch, in which 

 the eggs are hatched. 



The Oniscus, common Wood-louse, or Slater, is a ter- 

 restrial Isopod. It is an oval jointed creature, which 

 rolls itself into a ball when touched. The second of its 

 six pairs of posterior limbs perform the part of lungs : 

 they contain hollow organs in their interior, into which 

 the atmospheric air penetrates directly through openings 

 in their exterior covering: so the Oniscus and its con- 

 geners, which live on land, are drowned when put into 

 water. 



In the swimming Isopods, the five first pairs of tail- 

 limbs are false feet, and are suspended under the tail. 

 The gills, consisting of two great oval leaves, are fixed to 

 them by a stalk ; and are dragged through the water. 

 This group is very numerous ; many live among the sea- 

 weeds on the coasts, others perforate submerged wood 

 in all directions, and live in the winding galleries they 



