22 A MANUAL OF ZOOLOGY 



a long tendon extending obliciuely downward to its Inser- 

 tion on tlie mandible. What motion is given to the man- 

 dible by this muscle? Look for small muscles extending 

 to the antenna. 



Remove the great chela from the body. Note the 

 m^uscles of the basal joints. To what- are they attached? 

 With a pair of bone forceps cut around the edge of the 

 pincher and lay off the exoskeleton on one side. Note 

 the muscle contained in the cavity. Carefully dissect 

 away the muscle and find its origin and its Insertion. 

 Note the central tendon and the direction of the muscle 

 fibers. What motion does it produce? Notice another 

 muscle just opposite this one and demonstrate its motion. 

 Why should one be called the adductor and the other the 

 abductor?" Which is which? Study the muscle teased out 

 in normal salt solution. Stain and note results. Draw. 



At the anterior end of the superior abdominal artery, 

 find the pericardial sinus. Note Its shape and its size. 

 Cut through the mid-dorsal line, fold the parts back, and 

 find the heart. Note its size and shape. How is the heart 

 fastened to the sinus? Look for openings into the heart 

 on the dorsal, the lateral, and the ventral surfaces. How 

 n^any are found on each? What connection does the 

 superior abdominal artery have with the heart? The 

 opiithalmic artery originates from the anterior end of the 

 heart. Trace it towards the head. Does it have branches? 

 The antennary arteries leave the heart, one on either side 

 of the ophthalmic artery. Branches from these arteries 

 supply what organs? The hepatic arteries arise from the 

 antero-ventral part of the heart. The sternal artery 

 arises from the posterior end of the heart, ventral to the 

 superior abdominaj artery. Notice that it divides soon 

 after leaving the heart. What direction do the branches 

 take? Sketch the circulatorj;_ system in an^utjine drawing 

 pf the3Bimalr KilTa specimen and take some' blood from 

 thig-'perioardial sinus and examine with the microscope. 

 Note its color and account for the same. 



THE DIGESTIVE SYSTEM— Dissect away the gills 

 and other organs on one side to expose the stomach. 

 What 'is its shape and position? Are there muscle fibers 

 extending from the stomach to any other part of the body? 



