362 Introduction to Animal Morphology. 



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

 3. Cymothoidae feet (the three anterior pair in ^Ega) with 

 claws ; antennae large ; maxillipede operculate ; head small ; 

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

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

 Family 4. Sphaeromidae 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. 



