144 ARTHROPODA. 



Huxley: The Crayfish. An Introduction to the Study of Zoology. 1884. 



Mead: Habits and Growth of Young Lobsters. Rhode Island Com. In- 

 land Fisheries, 21, 1901. 



Pearl and Clawson: Variation and Correlation in the Crayfish. Carnegie 

 Inst. Pub., 64, 1907. 



Pearse: Observations on Copulation Among Crawfishes with Special Refer- 

 ence to Sex Recognition. Am. Nat., 43, 1909. 



Steele: Regeneration of Crayfish Appendages. Univ. Missouri Studies, 2, 

 1904. 



: Regeneration in Compound Eyes of Crustacea. Jour. Exp. Zool., 5, 

 1907. 



Williams: The Stomach of the Lobster and the Food of Larval Lobsters. 

 An. Rep. Com. Inland Fish., Rhode Island, 37, 1907. 



CALLINECTES HASTATUS. (Blue Crab.) 



Crabs may be found in shallow water along shore, where they 

 may be easily observed on quiet days. In what direction does 

 the animal normally move? How are the legs used? What is 

 the attitude of defense? Determine how the blue crab swims. 

 What do crabs apparently use for food? Do they conceal them- 

 selves, are they protectively colored, or do they depend entirely 

 upon their weapons for defense ? 



In studying the anatomy of the crab, constant comparisons 

 should be made with the lobster. 



External Anatomy. 1. The body is composed of cephalb- 

 thorax and abdomen. Dorsally note the shape of the carapace 

 and the position of the abdomen. The size of the abdomen 

 differs in male and female. Why should it be larger in the 

 female? 



2. Note the antennce, antennules, and eyes, and see how they 

 are packed away in recesses in the carapace. In the living 

 animal see if any of these are frequently moved. 



3. The third maxillipeds are flattened and cover the other 

 mouth appendages. 



4. Straighten the abdomen and note the anus. Compare the 

 abdomen of a male with that of a female and both with that of the 

 lobster. The dorsal side of each segment is covered by a tergum. 

 The covering between each pair of pkopods is the sternum, the 

 immovable flap lateral to them is the pleuron. Compare the ab- 

 dominal appendages or pleopods of a male and a female. 



