146 NATUKK STUDY 



Crabs. 



Crabs n:ay also be obtained at the market. There is an 

 abundance of small crabs to be found along the marshes and 

 creeks coming into the ocean. If some of these are placed in ajar 

 half filled with sand moistened with sea water, they will remain 

 alive some time, will burrow in the sand and their motions and 

 habits may be studied. 



The study of the parts of the crab will show it to be of the 

 same plan and structure as that of the shrimp and lobster. The 

 cephalo-thorax is, however, very broad, and the abdomen very 

 small and narrow and folded up under the cephalo-thorax. 



Have the pupil compare the three limb by limb. Prepara- 

 tions of each of these make interesting additions to the museum. 

 These forms are of the group Crustacea. 



After the above forms are studied, a good lesson niay be 

 made by comparing the structure of a shrimp and an insect 

 (grasshopper or beetle). 



Clams. 

 Clams may be obtained in the market, or, as some of the 

 pupils well know, by digging in the mud at low tide in certain 

 situations. The clams buried in the mud have what are called 

 "long necks." This is a projection reaching from the body ofthe 

 clam, as it is buried some inches below the surface of the mud. 

 It contains two tubes, one of which brings water to the body of the 

 animal, while the other carries a stream of water away from the 

 body. Tlie animal may thus hide away in the mud and 3'et have 

 a current of sea water loaded with oxygen and the fine particles of 

 food on which it lives flow thru it, passing its mouth and over its 

 gills. In the study of the body, the sliell, its hinge, its muscles, the 

 body, the gills and the "foot," are to be looked for. In some 

 of the higher grades these points in structure may be made out, 

 and then tlie pupils led to find the same, if they can be detected, 

 in mussels and ovsters, forms without the "neck." 



