50 INVERTEBRATE ZOOLOGY 



CRUSTACEA 



A CLADOCERAN PHYLLOPOD. DAPHNIA 



This is a small freshwater crustacean common in lakes and 

 pools. It should be studied under the microscope and alive 

 if possible. Place several on a slide under a cover-glass and 

 draw off enough water to keep them quiet; also observe sev- 

 eral in a watch-glass in order to see them from above. The 

 body of the animal will be seen to differ in shape from those 

 crustaceans already studied. It is but indistinctly segmented, 

 and, except the head, is entirely covered by a bivalve shell. 

 This shell is the cuticular covering of paired folds of the 

 dorsal integument, one fold covering each side of the body. 

 Beneath the opening of the valves of the shell appear the 

 appendages and the abdomen ; on the surface of the shell a mesh- 

 work of fine lines can usually be seen. Notice the large, 

 median eye; it may often be seen to tremble slightly. The 

 shell has a deep, ventral indentation near the base of the 

 antennae. 



The first pair of antennae is very small, but may be easily seen 

 projecting downward just 'back of the eye. The second pair of 

 antennae is very long and biramous, the two branches being the 

 exopodite and endopodite ; they are the principal organs of 

 locomotion. Just back of the antennae is a large flap, called 

 the upper lip, and back of this are the large mandibles. There is 

 but a single pair of maxillae, and they are so small that they will 

 probably not be seen. Four to six pairs of thoracic appendages 

 follow, the function of which is probably exclusively respira- 

 tory. How many are present in your specimen? Notice 

 the leaf-like surface of these appendages (whence the name 



