THE INVERTEBRATE COURSE. 127 



VII. 



LABORATORY WORK ON LIMULUS : DR. R. H. BOWEN, DR. C. L. 

 PARMENTER AND MR. D. B. YOUNG. 



In addition to the work outlined in Drew's manual, the follow- 

 ing studies can be readily and satisfactorily made: 



I. Method of Feeding. Place a large Linuilits on its back and 

 wait until it is perfectly quiet. Then place bits of mussel, drops 

 of fluid from a macerated mussel, and bits of Nereis on the spiny 

 bases of the legs and note the role played by each appendage. 



II. Dissection. A longitudinal section of Limuhts cut just a 

 little to one side of the median plane shows that the, various 

 organ systems are arranged in layers. Suspended from the dor- 

 sal carapace is the tubular heart surrounded by the pericardium. 

 Below the heart is the d/igestive tract. This consists of the 

 esophagus, a tube which leads forward to the stomach or proven- 

 triculus, which turns upward and backward and opens into the 

 straight intestine. At the junction of the esophagus and pro- 

 ventriculus is a plate of skeletal material, the endocranium, which 

 continues back through the cephalothorax. Below this internal 

 support is the central nervous system. Such a dissection, al- 

 though useful, does not show the various organs as well as does 

 a dorsal view. Therefore the following method is advised. 

 Students will work in pairs and trace out in succession the vas- 

 cular, the digestive, and the nervous systems. 



i. For dissection use adult, live animals not over 10 to 12 

 inches across the carapace. The larger ones have a very strong 

 exoskeleton to cut through. Place the animal on its back. Cut 

 off the legs leaving the coxal joint attached to the body. Cut 

 around the carapace as shown by the dotted Hue in Fig. 2. Use 

 a heavy knife, such as a w r ell-worn oyster knife. Begin at the 

 point marked " I " and keep well in from the edge to avoid the 

 strong trabeculre which pass dorso-ventrally along the border. 

 Then go back to the abdomen and make the cuts marked " 2 " 

 and " 3." After this cut through the interarticular membrane on 

 the dorsal s'ide of the caudal spine. 



The spine and ventral piece of exoskeleton may then be lifted 

 up from the dorsal carapace and the cuts " 2 " and " 3 " carried 



