37^ THE CRAYFISH cfiAr, 



sternal and ventral alxlnminal arteries (p. 375) will be seen, the sternal 

 artery passing between the connectives joining the fifth and sixth 

 postural ganglia. 



2. The brain gives off nerves to the eyes and the two pairs of 

 feelers : ijie siiljo^sophageal ganglion supplies the mandibles and 

 four following pairs of appendages with their segments. Each of 

 the other ganglia supplies one segment (with its appendages) only, 

 except in the case of the last or 6th abdominal ganglion, which 

 gives off nerves to the telso]i. (A sniall aiilcnor visceral ncrz'e^ 

 arising from the brain and resophageal connectives and supplying the 

 fore-gut, will ha\'e been removed, and a small posterior visceral 

 iicrvc, supplying the hind-gut, arises from the last abdominal 

 ganglion.) .Sketch. 



V. The ank'iinary ox green-glands a.xe situated just behind the ba.ses 

 of the large feelers. Blow through the renal aperture i)f one side (p. 373) 

 and note the duel and urinary hladifer on the dorsal side of the gland, 

 Then cut through the duct, remove the whole gland, and examine under 

 water, Sketch. 



!*• The Appendages. — Remove the appendages of one side, 

 lieginning with the last, one b)- one, cutting through the articular 

 n^embrane with a scalpel, and then taking hold of the basal joint with 

 the forceps and pulling the appendage away. Work through the de^ 

 scription on pp. 350-353 and sketch typical appendages from each region. 

 Note the delicate faragtiaflia behind the mouth and the lahntnt 

 in front of it (p. 356). 



The arrangement of the joints and muscles of the limbs can be well 

 seen by examining the large first leg or cheliped. Note that each joint 

 works in a different plane, and then cut away the exoskeleton 

 from one side of the two or three distal podomeres, .so as to 

 expose the muscles (compare Fig. 85). Then remove these, and note 

 their chitinous tendons. Observe that the flexor muscle and its tendon, 

 which moves the pincers, is much larger than the extensor muscle, 



E. Sensory Organs. 



1. Tactile organs. Snip off some seta; from the body or appendages. 

 Examine under the microscope. Sketch. 



2. " Olfaclory'^ organs. Examine the outer flagellum of the 

 antennule under the low power, and note the tufts of .spatula-like 

 olfactory setce on the ventral surface. Sketch. 



3. Auditory organ. Carefully cut away the convex ventral side of 



