190 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



a row of hairs which cover a small slit, the opening of the 

 auditory organ. 



11. The large eyes, mounted at the tips of movable 

 cylindrical eyestalks. 



12. Make sketches of the series of appendages. 



XX. THE GENERAL ANATOMY OF A CRAB. 



( CalUnectes hastatus. ) 



Either fresh or alcoholic specimens may be used for 

 dissection ; l)ut if fresh specimens are used, the various 

 parts may be rendered more conspicuous by covering the 

 specimen with alcohol after it has been opened. All the 

 dissecting should be done under water or alcohol. 



I. General Anatomy. 



Select if possible a large female specimen ; kill it by 

 bleeding ; and open it by carefully cutting away the dorsal 

 portion of the carapace, taking care to avoid injuring the 

 internal organs. 



a. In the specimen thus opened notice the tough, dark- 

 colored skin, which lies just inside the shell and lines it. 

 Cut away this skin or turn it out and notice : — 



b. The large transparent stomach (Fig. 100, e) which 

 occupies the middle of the anterior half of the cavity of 

 the shell. It is pear-shaped in surflice-view, with its ante- 

 rior end broadest. Notice that the outer ends of the 

 anterior l)order are prolonged into a pair of horn-like pro- 

 cesses, which are attached by muscular fibres to the inside 

 of the anterior edge of the carapace, behind the orbital 

 notches. 



c. A pair of calcified rods, the pterocardiac ossicles 

 (Fig. 100, b) lie transversely across the dorsal surface of 



