148 INVERTEBRATE ANIMALS. 
is firmly cemented to the centre of a membranous or shelly 
plate. The body is enclosed in a limpet-shaped or conical 
shell, composed of several pieces, and having an aperture at its 
summit. This opening is closed by a movable lid, and from it 
the animal can protrude its delicate legs or “cirri,” which look 
like a “glass hand,” and are constantly employed in sweeping 
the water in search of food. 
- In accordance with the fixed condition of the adult, almost 
all the Czvréfedia are hermaphrodite, possessing both male and 
female organs of reproduction. In some cases, however, males 
exist, but these are much smaller than the females, and quite 
different to them in appearance, and they spend their existence 
within the shell of the female. 
APPENDIX, GIVING THE REMAINING ORDERS OF CRUSTACEA. 
Order Rhizocephala.—Minute Crustaceans, free when young, but 
when adult parasitically attached to the abdomen of various crabs. 
When adult they are completely deformed, destitute of limbs, and 
attached to their host by means of numerous branched tubes or roots 
which ramify deeply among the internal organs. Ex. Peltogaster. 
Order Ichthyophthira.—Minute Crustaceans, free when young, but 
when adult parasitic upon various kinds of fishes; adult usually de- 
formed and soft ; young with eyes and swimming-feet. Lx. Lernea. 
Order Phyllopoda.—Thoracic feet leaf-like and acting as branchiee. 
ix. Apus. 
Order Lemodipoda.—Kyes sessile ; abdomen rudimentary ; respira- 
tion by means of little vesicles attached to the thoracic segments or 
legs. £x. Cyamus (the whale-louse). 
Order Amphipoda.—Kyes sessile ; abdomen well developed ; respira- 
tory organs in the form of vesicles attached to the thoracic limbs. £2. 
Sandhopper (Zadtrus); Fresh-water shrimp (Gammarus). 
Order Stomapoda.—Eyes stalked ; gills unprotected, usually suspended 
beneath the abdomen. 4x. Locust-shrimp (Sgzz//a). 
