28 A MANUAL OF ZOOLOGY 



of the protractor pedis muscle. In marine forms the 

 scars are not all distinct. 



Note. the siphons. How many are there? What is 

 their shape, and size? Are they separate tubes? Tuyn 

 back one of the lobes of the mantle and note the paiial 

 cavity. The large vehtral cavity is the brancliial cavity, 

 and the small dorsal cavity is the cioacai cavity. What 

 is the relation of the abdomen to the muscles and to the 

 foot? Compare the texture of the foot with that of the 

 abdomen. What direction dpes the foot take when ex- 

 tended? Note the gills, or gill-plates. How many are there? 

 The supra-branchial chamber Is laid open when a slit is 

 made along the attachment of the outer gill and the man- 

 tle. Demonstrate the following in the structure of a gill: 

 the water tubes, the inter-lamellar junctions, and the 

 inhalent apertures. Sections will be needed. Study the 

 ciliary action on the gill split open. Make a drawjng 

 to_sh03v--tlie_structure-T3f~th:6''gnL" 



Find the mouth and note its size, shape, and position. 

 How do the labial palpi compare with those-on the lobster? 

 Into which siphon does the anus open? It Will require 

 care and patience to work out the digestive system. From 

 the mouth trace, the oesophagus. What is its direction? 

 The liver wiil appear as a dark colored mass around the 

 stomach and the oesophagus. How is the stomach dls- 

 ■ tinguished from the oesophagus? The bile duct opens into 

 the oesophagus near tl^e stomach. Trace the intestine 

 from the stomach through the yellowish white generative 

 gland. Note that the rectum passes through the pericardial 

 cavity. Note the typhlosoie, a prominent ridge on the' 

 ventral side of the rectum. Where has this organ been 

 seen on previous specimens? Make an outline drawing 

 of the body and place a diagram" of th? digestive system 

 iir~tlrErsame. -- — - 



THE CIRCULATORY SYSTEM— Carefully remove a 

 living specimen from the shell. The movements of the 

 heart may be observed. Open the pericardium and study 

 the heart. Note the median ventricle and the two lateral 

 fan-shaped a'uricles: The intestine was traced through 

 the ventricle in the other specimen. Trace the .anterior 

 and the posterior aorta, the former above, and the latter 



