CRUSTACEA OF THE LAND 201 



segments which form the " peduncle," a " flagellum " 

 of about twelve short segments. The uropods or 

 tail appendages are long, each with two slender, 

 pointed branches. On the under - side of the 

 abdomen can be seen the five pairs of pleopods, each 

 with two plate-like branches attached to a very short 

 peduncle. As in most aquatic Isopods, the plates of 

 the pleopods are soft and thin, and appear adapted 

 to act as gills, although the outer plate of each pair 

 is somewhat stiffer than the inner. The Sea-slater 

 is generally found just above high-water mark, prob- 

 ably always within reach of the salt spray, and it is 

 said sometimes to enter the water of rock-pools. 



In almost every garden there may be found, under 

 flower-pots and the like, a Woodlouse, about two- 

 thirds of an inch long, of a brown colour, with 

 yellowish blotches arranged in a row on each side of 

 the back. This is Oniscus asellus, a species widely 

 distributed in Europe and North America. It has 

 the antennae shorter than in Ligia, and the flagellum 

 is composed of only three segments. The uropods 

 are quite short. The endopodites of the pleopods 

 are membranous gill-plates, which serve for respira- 

 tion in the moist air in which these animals generally 

 live. The exopodites are stiff plates which cover and 

 protect the delicate endopodites ; it is probable that 

 they also aid in respiration, for they contain a 

 system of minute channels, filled with air, where the 

 cuticle is separated from the underlying cells. As 



