132 ARTHROPODA. 



forward by pressing aside the muscle mass. In the male the 

 testis is a slender, white, convoluted cord, which ends blindly 

 against the side of the stomach. The extent and position of the 

 far thicker yellow ovary is much the same (unless the animal 

 be mature, in which case it will be found greatly enlarged and 

 orange). 



2. The heart extends through the posterior third of the tho- 

 rax. Remove the upper part of the delicate pericardium sur- 

 rounding it, cut its arterial and other connections, and place it 

 in water. Note the shape, the origin of the arteries, and the 

 three pairs of valvular ostia. Do you understand how it receives 

 blood? 



3. Trace the gonads as far as the abdomen, noting the single 

 anastomosis between those of opposite sides just in front of the 

 heart. Beneath the heart the sexual ducts are given off — vasa 

 deferentia in the male, oviducts in the female. Trace one out- 

 w^arcl and downward to its opening by removing a portion of the 

 body- wall and of the basal joint of the proper leg. 



4. Remove the posterior lateral body-wall forward to a posi- 

 tion opposite the anterior third of the stomach. Pull the an- 

 terior lobe of the liver, which extends beneath the stomach, 

 outward and backward. The liver will be seen to be attached 

 to the pyloric end of the stomach (i. c, the smaller part, where 

 the stomach passes into the intestine). Cut this attachment 

 and note that it is really where the liver opens into the stomach. 

 Just back of this point the right and left lobes of the liver 

 are connected by a cross-branch passing beneath the intestine. 

 Remove one liver lobe back to the abdomen. After having the 

 circum-esophageal connectives pointed out, remove the stomach by 

 cutting the esophagus, the intestine, and the bands of muscles 

 attached to the stomach. Examine it in water, noting the cardiac 

 and pyloric parts, the chitinous grinding and straining apparatus 

 in the interior, and the muscles and plates that cause the move- 

 ments of the grinding apparatus. Why does a lobster with 

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



5. Between the circum-esophageal connectives medially and 



