142 ABTHROPODA. 



ments of the grinding apparatus. Why does a lobster with 

 chelse and six pairs of mouth appendages need a gastric mill? 



5. Between the circum-esophageal connectives medially and 

 the large antennary muscles laterally, note the oval excretory 

 organs, called the green glands. They are covered by a very 

 delicate membrane. Poke a small hole in one of 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 ccecum. 



Circulatory and Nervous Systems. 1 Remove the carapace 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 possible. 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 examine 

 it from the side, noting the great sternal artery extending down- 

 ward, and the smaller dorsal abdominal artery running back above 

 the intestine. Follow the latter through the abdomen. 



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. 



