SOW-BUGS AND BEACH-FLEAS, 
01 
bridges, where salt water has evaporated and become 
briny. 
Order 4. Tetradecapoda, — To this order belong the sow- 
bugs {Isopoda) and the beach-fleas (AmpJiipoda). They 
have no carapace, but the head is small, bearing two pairs 
of antennae, and a pair of jaws, and three pairs of maxillae. 
e ant ant^ 
Fig. 112.— Nauplius of Branchi- FiG.113.— Brine Shrimp(^r#emzaf;racz7/s), 
pus stagnalis. ant^, 1st an- seen from above, much enlarged, e, 
tenna; anf^^ 2d antenna; md, eye; ant, 1st antennae; ant^, 2d anten- 
mandible ; lb, under lip. Much nse ; mcZ, mandibles; mx, maxillae ; pes, 
enlarged. foot; o, ovisack. 
The thorax is continuous with the abdomen. They breathe 
by leaf-like gills, which are situated on the middle feet in 
the Amphipods, or on the hinder abdominal feet in the 
Isopods. The various species of Porcellio (sow-bug) live 
under stones on land;^nd allied to Asellus, the water sow- 
bug, is the marine Limnoria terebrans, which is very in- 
jurious to the piles of bridges, wharves, and any submerged 
