3°° 



COLLEGE ZOOLOGY 



Branchipus (Fig. 210, A), is a common fresh- water phyllopod; 

 Artemia (Fig. 210, B) is a genus found in salt-water lakes, such 

 as the Great Salt Lake of Utah. Daphnia ( Fig. 211) is a water- 

 flea (Cladocera) abundant in fresh-water ponds and lakes. 

 Its body is enclosed in a shell, and the second antennae {ant. 2) 

 are modified to form swimming appendages. During the spring 

 and summer only females are present, and at this time " sum- 

 mer " eggs are produced which develop parthenogenetically in 

 the brood-pouch {br.p) of the mother. In the autumn males 

 are developed; they fertilize the " winter " eggs, which are 

 larger and fewer in number than the summer eggs. 



The Ostracoda (Fig. 212) are bivalved Crustacea which 

 protrude their antennas (2) from the two valves of their shell and 

 use them as oars in swimming. They are common in ponds and 

 streams. 



A well-known fresh-water Copepod is Cyclops (Fig. 213), an 

 animal that has a single compound eye (e) in the middle of the 

 head. The antennae (/) are used for locomotion. The fe- 

 male may be recognized easily during the summer because of the 

 two brood sacs (8) full of eggs that she carries about with her. 



The subclass Cirripedia contains the barnacles (Fig. 214). 

 These are sessile Crustacea, many of which possess shells caus- 

 ing them to resemble mollusks. The larvae are free swimming 

 and resemble those of other Crustacea, but they pass through 

 a metamorphosis, during which some or all of the appendages 

 and other parts of the body are lost, and usually a calcareous shell 

 is formed. The rock-barnacle, Balanus balanoides (Fig. 214) 

 is abundant along the North Atlantic coast, where it lives at- 

 tached to rocks and other objects. The movements of the ap- 

 pendages create a current of water which brings food into the shell. 

 The goose barnacle, Lepas, has a bivalve shell and is attached by 

 a peduncle. Sacculina is a barnacle parasitic on the crab, Car- 

 cinus, and in the adult stage resembles a tumor, consisting almost 

 entirely of reproductive organs. Most barnacles are herm- 

 aphroditic. 



