362 Introduction to Animal Morphology. 



no segmentation, but has a segmented free-swimming young. 

 3. Cymothoidse — feet (the three anterior pair in M.%^ with 

 claws ; antennae large ; maxillipede operculate ; head small ; 

 mostly parasites on the gills of fish (Cymothoa), or free 

 (Serolis, &c.) The young Cymothose are free-swimming. 

 Family 4. Sphaeromidas — broad, shield-like, littoral ; antennae 

 two pair, arising close together ; head large transversely ; legs 

 simple ; front ring of post-abdomen rudimental, united to- 

 gether ; a swimming tail in some ; they can roll themselves 

 into a ball, except Cymodocea. Monolistra, from Adelsberg 

 cave, is blind. Family 5. Oniscidae (millepedes, slaters) — 

 under stones in damp, not wet, places ; oval, with rudimental 

 or no antennules and mandibular palps ; flat maxillipedes ; feet 

 all equal, ambulatory ; post-abdomen six-jointed ; its last seg- 

 ment with the pleopods modified into lamellae or bristles ; 

 the foremost gill spaces have openings through their epipodial 

 opercula, leading into canals, which are a form of tracheae 

 whereby air enters ; the body is flatly compressed, not invo- 

 luble, in Oniscus and Porcellio, and pointed behind in Ligia. 

 Armadillo is more convex, capable of rolling into a ball, the 

 last pleiopod with a large (in Armadillidium a small) basal 

 joint. The recurrent nerve in Oniscus has an azygos ganglion 

 frontale, as in Insects and Myriopods. Family 6. Idoteidae, 

 box slaters — body long, equally broad, cylindrical (Arcturus), 

 or compressed (Idotea) throughout, with a short antennule, 

 but no mandibular palp ; post-abdomen with no posterior 

 tail process. Family 7. Asellidae — body as in last, but with a 

 long posterior process on the shield-like hinder segment. 

 Asellus is the freshwater millepede. Limnoria terebrans de- 

 stroys submerged wood. The cylindrical Tanais has the first 

 and second thoracic rings fused to the head. 



