HOMARUS 173 



the membranes and with a blowpipe show that it is really a 

 thin bladder. Its opening on the antenna has already been 

 seen. 



6. Remove the dorsal wall of the abdomen and trace the 

 posterior portions of the gonads, liver lobes, and intestine. 

 In the sixth abdominal segment the intestine swells to form 

 the chitin-lined rectum and gives off the blind intestinal 

 caecum. 



Circulatory and Nervous Systems. 1 — Remove the cara- 

 pace of an injected specimen as before, also the gill cover and 

 gills on one side. 



1. There can generally be seen, through the transparent 

 body wall, efferent branchial veins, which return the blood 

 from the gills. These unite into six large ones which open 

 into the pericardium at the side. Find these openings if pos- 

 sible. Do you understand how blood gets into the heart? 



2. Note, at the anterior end of the heart, the ophthalmic 

 artery and the two antennary arteries. Trace the former 

 forward to the rostrum, cut it on the stomach and turn it 

 forward for future study. Trace the antennary arteries to 

 the mandibular muscles and cut them near the heart. Press 

 the front end of the heart back and note the two small 

 hepatic arteries. Each branches immediately, one division 

 passing between the gonads, and the other laterally. 



3. Remove the muscles on one side of the heart and ex- 

 amine it from the side, noting the great sternal artery ex- 

 tending downward, and the smaller dorsal abdominal artery 

 running back above the intestine. Follow the latter through 

 the abdomen. 



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



1 The circulatory system of a fresh specimen may be satisfactorily 

 injected with starch mass by inserting the needle of a hypodermic 

 syringe into the pericardium from the posterior margin of the carapace. 

 The operation is easily performed when the distance to the pericardium 

 is understood. The carapace may be cut away and the needle inserted 

 directly into the heart if preferred. 



