IV 



and abdomen are thus enclosed and the carapace is always very delicate and transparent. 

 The order is essentially confined to fresh-water and the few marine forms are monstrosities 

 In spite of the extreme delicacy of the organization of these animals, they are among the 

 most abundant denizens of quiet bodies of water. Like plant-lice and a few other in- 

 sects the cladocera are parthenogenetic and frequently pass through a sort of alternation 

 of generations, the final stage of which is sexual and produces resting eggs, commonly 

 protected by a case or ephippium, produced by the modification of the valves of the shell 

 of the parent. This order and the Phyllopoda are best adapted of all Crustacea for illus- 

 tration of many important physiological and anatomical facts. 



The Copcpoda are microscopic Crustacea even more abundant than either of the 

 above-mentioned orders both in inland and pelagic situations. They may be recog- 

 nized by the elongated multi-articulate body terminating with two stylets and furnished 

 with cylindrical setose pairs of limbs attached to the thoracic segments beneath. The 

 female generally bears the eggs in a pouch below the abdomen. Alabama has added 

 her quota to the knowledge of this group also. Various species occur in almost incred- 

 ible numbers in the waters of the gulf, while it is impossible to secure a gathering from 

 pond or river not peopled by one or more species of the fresh-water genus Cyclops. 



The Phyllopoda are larger than the animals of any of the previously mentioned or- 

 ders and curiously mimic in some cases the Ostracoda or Cladocera and in others the 

 Copepoda. From any of these all species are easily recognized by the many (from 10 to 

 20 pairs of) foliaceous swimming feet. The shell-less species are often very beautiful and 

 are especially interesting because of the fickleness of their appearance and equally sud- 

 den disappearance. The eggs of many species will only germinate after a period of 

 dessication and then the young seem to fall with the rain, as tadpoles are popularly 

 thought to do, so rapidly do they develop. 



In the waters of the gulf a few representatives of the Cirrepedia or barnacles may be 

 found. These acorn-shells, long supposed to be mollusks, and at one time seriously re- 

 garded as a stage in the development of water-fowl, may be collected upon the piers and 

 rocks along the shore. 



Passing now to the higher Crustacea or Mallacostraca (as distinguished from the al- 

 ready mentioned, often collectively called Entomostraca,) we find examples of the fol- 

 lowing orders: Order Amphipoda contains laterally compressed and rather small species 

 of fourteen-footed Crustacea, illustrated by the sand-fleas so abundant along shore and 

 recognized by their enormous leaps. Order Isopoda resembles the above and like it has 

 sessile eyes, but the body is depressed and many species are adapted (as the sow-bugs) 

 for terrestrial habitation. Among the ten-footed or Decapod Crustacea the order Mac- 

 rura is illustrated by the cray-fish and shrimp, while the crabs of various species con- 

 fute the order Brachvura. 



The student in using this list is requested to turn first to the key at the end of the paper, by means of which any group 

 here described may be identified by use of the key and the references to pages in the body of the paper. The key will not ap- 

 ply to species not contained in the list and is largely artificial. For means of more careful study the student must have recourse 

 to special memoirs such as the following: 



The various publications of the United States Fish Commission illustrate the most characteristic species of the higher or- 

 ders. Dr Packard's monograph in Hayden's Twelfth Geological Report covers the Phyllopoda. Various papers by Birge and 

 Forbes, and the writers' monograph in the twelfth annual of the Minnesota Geological survey, elucidate the fresh-water Entomos- 

 traca The American Cirripedia still await elaboration as well as the marine Copepoda and most of the Ostracoda. 



