138 INVERTEBRATE ANIMALS. 



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 OP 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 deformed and 

 soft ; young with eyes and swimming-feet. Ex. Lerncea. 



Order Phyllopoda. Thoracic feet leaf-like and acting as branchiae. Ex. 

 Apus. 



Order Lcemodipoda. Eyes sessile ; abdomen rudimentary ; respiration 

 by means of little vesicles attached to the thoracic segments or legs. Ex. 

 Cyamus (the whale-louse). 



Order Amphipoda. Eyes sessile ; abdomen well developed ; respiratory 

 organs in the form of vesicles attached to the thoracic limbs. Ex. Sand- 

 hopper ( Talitrus) \ Fresh-water shrimp ( Gammdrus). 



Order Stomapoda. Eyes stalked ; gills unprotected, usually suspended 

 beneath the abdomen. Ex. Locust-shrimp (Squilla). 



