174 ARTHROPODA 



tennaries through the mandibular muscles, noting the branch 

 to the stomach. 



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

 cumesophageal connectives forward and identify the cerebral 

 ganglia in order not to destroy them. 



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

 tennary 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 connectives. In the thorax the ventral nerve chain passes 

 beneath a system of chitinous plates {the endophragmal 

 skeleton) and lies in a cavity, the ventral blood sinus. Note 

 the enlarged subesophageal ganglion, the cross commissure 

 just back of the esophagus, the nerves to the mouth ap- 

 pendages, nerves from the cerebral ganglia, and nerves from 

 the other ganglia. What indication is there that the sub- 

 esophageal ganglia represent more than a single pair? 



Draw the nervous system. 



9. The sternal artery passes through the ventral nerve 

 chain and then extends backward and forward as the ventral 

 longitudinal artery. Remove the nervous system and follow 

 this artery. 



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. Smith- 

 sonian Cont. to Knowl., 35, 1907. 



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



Bumpus: Movements of Certain Lobsters Liberated at Woods Hole. 



Bull. U. S. Com. Fish., 1899. 



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



Herrick: Natural History of the American Lobster. Bull. U. S. Bur. 



Fish., 29, 1909. 



