SOW-BUGS AND BEACH FLEAS. 91 



bridges, where salt water has eTaiwrated and become 

 briny. 



Order 4. Tetradecapoda.~To this order belong the sow- 

 bugs {Isopoda) and the beach-fleas {AmjMpoda). They 

 have no carapace, but the head is small, bearing two pairs 

 of antennse, and a pair of jaws, and three pairs of maxillaj. 



ant ant^ 



Fig. 112.— Naupliiis of BranchU 

 pus stagnalis. ant^, 1st an- 

 tenna; anP, 2d antenna; md, 

 mandible ; lb, under lip. Much 

 enlarged. 



Fig. 1 13.— Brine SYiTivaT^iArtemia graa'Us), 

 seen from above, much enlarged, e, 

 eye; ant, 1st antenna); an(*, 2d anten- 

 Ties;md, mandibles; mx, maxillai;pes, 

 foot; 0, ovisack. 



The thorax is continnons 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;jind 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, 



