HOMARUS AMERICANUS. 143 



4. Cut all arteries and remove the heart. Trace the anten- 

 naries through the mandibular muscles, noting the branch to 

 the stomach. 



5. Remove the thoracic viscera as before, follow the circum- 

 esophageal connectives forward and identify the cerebral ganglia 

 in order not to destroy them. 



6. Follow one antennary artery to the green gland, antennary 

 muscle, eye muscle, etc. 



7. Follow the distribution of the ophthalmic artery. 



8. Remove the intestine and muscles of the abdomen, and find 

 and trace forward the ventral nerve chain. Notice the position 

 of the ganglia and the nerves that leave them and the connec- 

 tives. In the thorax the ventral nerve chain passes beneath a 

 system of chitinous plates (the endo-phragmal skeleton) and lies 

 in a cavity, the ventral blood sinus. Note the enlarged sub- 

 esophageal ganglion, the cross commissure just back of the esoph- 

 agus, the nerves to the mouth appendages, nerves from the 

 cerebral ganglia, and nerves from the other ganglia. What indi- 

 cation is there that the sub-esophageal ganglia represent more 

 than a single pair? 



Sketch the nervous system. 



9. The sternal artery passes through the ventral nerve chain 

 and then extends backward and forward as the ventral longitu- 

 dinal artery. Remove the nervous system and follow this ar- 

 tery. 



Draw a diagrammatic cross-section through the thorax, putting 

 in one drawing the circulation from the heart through the sternal 

 artery to the limbs and back through the gills to the heart. 



Andrews: The Keeping and Rearing of Crayfish for Class Use. Nat. 



Stud. Rev., 2, 1906. 

 : The Young of the Crayfishes Astacus and Cambarus. Smithsonian 



Cont. to Knowl., 35, 1907. 



: Conjugation in the American Crayfish. Am. Nat. 29, 1895. 



Bumpus: Movements of Certain Lobsters Liberated at Woods Hole. Bui. 



U. S. Com. Fish, 1899. 



: Embryology of the American Lobster. Jour. Morph., 5, 1891. 



Herrick: Natural History of the American Lobster. Bui. U. S. Bur. Fish, 



29, 1909. 



