190 ELEMENTARY BIOLOGY. [CUA] 



. LABORATORY WORK. 



Crayfish are best killed under chloroform, proceeding a^ 

 with the Frog. (p. 35). They may be best kept ahve in 

 moist atmosphere near running water, fed upon soppe( 

 bread. A sink, covered with a sheet of glass, meets al 

 requirements. 



A. General external characters. 



The animal is covered by a continuous exoskeleton whicl 

 is for the most part calcified, the following parts ar| 

 readily recognised : — 



a. The body proper: 



a. Its anterior unsegmented portion {cephalothc 

 rax): the great shield-like plate {carapacei 

 covering the back and sides of the cephalothc 

 rax; the groove across the carapace (cervical 

 suture) marking out the line of junction of head 

 and thorax: the anterior prolongation of the 

 carapace to form the rostrufn orfrofital spine. 



p. Its posterior segmented portion {ahdomen)'. its 

 seven divisions; the anterior six much like one 

 another; the most posterior [telsoti) different 

 from the rest (Cf. p. 174). 



b. The jointed limbs {appendages) attached to the 

 ventral aspect of the body: their varying characters 

 in different regions. 



c. The external apertures of the body. 



a. The mouth; seen on turning aside the append- 

 ages beneath the head. 



