168 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



XYIII.— THE STUDY OF THE HARD PARTS OF 

 THE COMMON CRAB. 



{Callinectes hastatus.) 



A STUDENT of the elements of Morphology can hardly 

 grasp the significance of the structure of the Decapod 

 Crustacea until he has studied several forms, and as excel- 

 lent directions for studying the crayfish or lobster are 

 within the reach of most students, it seemed best to de- 

 scribe some other type here. If the student has verified 

 the description of the crayfish or lobster which is given 

 by Huxley, Packard, or Huxley and Martin, the study 

 of a crab will serve as a review, and will throw new light 

 upon the significance of the facts. For the benefit of 

 those students who have not gone over this ground, I shall 

 give, in the next section, a brief description of the hard 

 parts of the lobster, and a lobster or a crayfish should, if 

 possible, be examined at the same time that the crab is 

 studied. 



If squilla can be procured, it should also be examined 

 at the same time, but as it is not readily procurable, I give 

 no description of it. 



The common edible crab may be found in abundance in 

 all the inlets, bays, and sounds of our southern coast; 

 and as it may also be obtained, during the winter, in the 

 markets of our larger cities, it is a good form to select for 

 laboratory work. If it cannot be procured, any other 

 crab will answer nearly as well, and most of the points 

 may be verified in the common shore crab (Cancer irrora- 

 tus) of the New England coast. This latter crab may be 

 collected in the crevices of rocks near low tide mark, and 



